Introduction to 9i SQL Handbook• Oracle server supports ANSI standard SQL and contains extensions• SQL used to communicate server to access, manipulate and control data• SQL SELECT STATEMENT CAPABILITIES: PROJECTION, SELECTION, JOINING• SELECT* from orders; Use this statement to retrieve data from a data table for Viewing/Inserting• KEYWORD USED IN UPPERCASE NO USE OF ABBREVIATION OR SPILT ACROSS LINES• CLAUSE SEPARATE LINE• SQL STATEMENT USED BY 1 OR NORE LINE NOT CASE SENSETIVE UNLESS INDICATED• INDENTS USED TO MAKE CODE MORE RELIABLE• ARTIHMETIC EXPRESSIONS/OPERATOR BY PRECEDENCE * / + -• DATE & CHARACTER LITERAL IN ‘02-12-2006’ single quotes• DISTINCT TO ELIMINATE DUPLICATE ROWS• SQL*Plus commands are used to manipulate data in tables, to manipulate table definitions in the database.• ISQL*PLUS ORACLE TOOL • DESCRIBE Isql*plus command• WHERE CONDITION TO LIMITING ROWS/SORTING ROWS/restrict ROWS• SQL*Plus feature used to replace values in WHERE clause? Ans.Substitution variables

COMPARISON CONDITIONS1. EQUAL TO =2. GREATER THAN > 3. GREATER THAN EQUAL TO >= 4. LESS THAN < 5. LESS THAN EQUAL TO <= 6. NOT EQUAL TO <> / ^= / !=7. BETWEEN A AND B ONLY 2 VALUES8. IN (SET) LIST OF VALUES9. LIKE A CHARACTER PATTERN10. IS NULL

WILDCARD SEARCH% DENOTES 0 OR MANY CHARACTER | _ DENOTES 1 CHARACTER [underscore]‘\_P%’ ESCAPE ’\’ [HERE ESCAPE CHARACTER \ ]LOGICAL CONDITION

1. AND2. OR3. NOT

PRECEDENCE OF OPERATOR1. Arithmetic2. Concatenation3. Comparison Cond.4. Is [not] null, like, [not] in5. [Not] between6. NOT LOGICAL CONDITION7. AND LOGICAL CONDITION8. OR LOGICAL CONDITION

Order by [asc] desc to sort rows in select statement/multiple columns/column also not in select [column list]Sort by column/column alias/column number. True regarding the ORDER BY clause?

• The sort is in ascending by order by default, executes at last after WHERE and GROUP BY clause • The ORDER BY clause comes last in SELECT statement, executes on server side as whole SQL

statementDUAL IS A DUMMY TABLE Functions

• Calculations on data• Modify individual data item• Manipulate o/p for group of rows• Format date and no to display

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Introduction to 9i SQL Handbook• Convert column data type• Always return values

Single Row Functions• return one value• act on each row returned• return one result per row• can be nested• arguments- columns or expressions• A single row subquery can retrieve only one row but many columns. • A single row subquery can retrieve data from more than one table. • SINGLE ROW FUNCTION NESTED TO ANY DEPTH

Argument• User supplied constant• Variable value• Column name• Expression

1. Character Functiona. Case Manipulation

Lower Upper initcapb. Character Manipulation

Concat SUBSTR LENGTH INSTR LPAD | RPAD TRIM REPLACE2. Number Function

ROUND TRUNC MOD3. Date Function

• Sysdate RETURNS CURRENT DATABASE SERVER DATE AND TIME• INTERNAL NUMERIC FORMAT 7 BYTES• CENTURY YEAR MONTH DAY HOURS MINUTES SECONDS• VALID DATE BETWEEN January 1,4712 B.C. TO December 31,9999 A.D.• DEFAULT DATE FORMAT DD-MON-RR 01-JUL-06• DATE + OR – NUMBER = DATE• DATE – DATE = DAYS• DATE+NUMBER/24 = DATE

a. MONTHS_BETWEENb. ADD_MONTHSc. NEXT_DAYd. LAST_DAYe. ROUNDf. TRUNC

4. Conversion DATA TYPE Functiona. IMPLICIT Function

i. VARCHAR2 OR CHAR TO NUMBER TO_NUMBERii. VARCHAR2 OR CHAR TO DATE TO_DATEiii. NUMBER TO VARCHAR2 TO_CHARiv. DATE TO VARCHAR2 TO_CHAR

FORMAT MODELTO_CHAR(DATE,’FORMAT MODEL’)TO_NUMBER(CHAR[, ‘FORMAT MODEL’]) TO_NUMBER(‘12345.52’,’$999999.99’)TO_DATE(CHAR[, ‘FORMAT MODEL’]) fx FOR EXACT MATCH TO_DATE(‘MAY 24, 2006’,’MONTH DD,YYYY’)TO_CHAR(NUMBER,’FORMAT MODEL’)9 0 $ L . , MI PR EEEE V B

b. EXPLICIT5. General Function

a. NVL(EX1,EX2) EX1 NULL PUT/RETURN EX2

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Introduction to 9i SQL Handbookb. NVL2(EX1,EX2,EX3) EX1 NOT NULL RETURN EX2 EX1 NULL RETURN EX3c. NULLIF(EX1,EX2) EX1 = EX2 RETURN NULL ELSE RETURN EX1d. COALESCE(EX1,EX2,…EXn) EX1 NULL RETURN EX2 EX1,EX2 NULL RETURN EX3

SELECT COALESCE (COMM_PCT,SALARY,10) COMMISSION FROM EMP;CASE COL/EXP WHEN IF_EXP THEN RETURN_EXP

ELSE ELSE_EXPEND ALIAS_NAMEDECODE (COL/EXP,

SEARCH1,RESULT1,SEARCH2,RESULT2,

DEFAULT_RESULT) ALIAS_NAMEUse: Select /where/order by with case and decode Multiple Row Functions

• A multiple row subquery can retrieve multiple rows and multiple columns. • A multiple row subquery can be compared by using the “>” operator (only case of all/any ). • The multiple-row subquery cannot be used with the comparison operator • A multiple-row subquery cannot be used in an INSERT statement to insert multiple rows at a time. • Group / AGGREGATE functions:

SET OF ROWS ONE RESULT PER GROUP, IGNORE NULL VALUES AUTOMATICALLY SORT RESULT IN ASCENDING ORDER Mix single row columns with aggregate functions in the column list of a SELECT

statement by grouping on the single row columns. Pass column names, expressions, constants, or functions as parameters to an aggregate

function. AVG NUMBER COUNT (*)/(EXPR)/(DISTINCT expr) (*) number of rows including duplicate rows [DATE] MAX NUMBER [DATE] MIN NUMBER [DATE] STDDEV NUMBER SUM NUMBER VARIANCE NUMBER

Format of using Group FunctionSelect / From / Where / [Having] Group by/Having /Order by;

Group by• Divide/spilt table info in groups• Grouping can be more than 1 column• Mix of individual item and group function must use a group by clause• Without group function can use a group by clause• Can use nesting group functions• Include columns in group by clause• If column not in select list still apply group by on this column• Using where exclude rows before divide into groups • Can’t use alias• AUTOMATICALLY SORT RESULT IN ASCENDING ORDER• To restrict groups or ROWS use having after/before group by clause don’t use where• Match criteria in having are displayed

Operator used in FunctionsSingle row

• EQUAL TO =• GREATER THAN > • GREATER THAN EQUAL TO >= • LESS THAN < • LESS THAN EQUAL TO <= • NOT EQUAL TO <> / ^= / !=

Subquery Retrieve data based on an unknown condition

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Introduction to 9i SQL HandbookMultiple row

• Subquery or inner query includes Where / Having/ From / Operator • Subquery in parenthesis ( )• RHS of comparison condition.• If Top-N analysis then order by needed otherwise not• Single row operator with Single row Subquery (return one row)• Multiple row operator with Multiple row Subquery (return multiple rows)• Executes sub queries first• Common Error: More than one row returned for a single row subquery

Single row operator with Multiple row sub query Use IN/NOT IN instead of =, LIKE, BETWEEN, IS, <> [can’t use]• *Comparison of two null values yields a null then where condtn. Is not true • in • any <any less than the maximum >any more than the maximum =any as IN• all <all more than the maximum >all less than the maximum <>ALL as NOT IN• not operator can be use with in any all<ANY EQUIVALANCEselect ename,sal,job from emp where sal<(select max(sal) from emp group by job having job='SALESMAN') and job !='SALESMAN';select ename,sal,job from emp where sal<any (select sal from emp where job='SALESMAN');>ANY EQUIVALANCE select ename,sal,job from emp where sal>(select min(sal) from emp group by job having job='SALESMAN'); select ename,sal,job from emp where sal>any (select sal from emp where job='SALESMAN');<All EQUIVALANCE select ename,sal,job from emp where sal<(select min(sal) from emp group by job having job='SALESMAN'); select ename,sal,job from emp where sal<all (select sal from emp where job='SALESMAN') ;> All EQUIVALANCEselect ename,sal,job from emp where sal< (select min(sal) from emp group by job having job='SALESMAN');select ename,sal,job from emp where sal> all (select sal from emp where job='SALESMAN') ;

Cartesian productJoin condtn omitted/invalidAll rows in 1st table joined to all rows in 2nd table

Type of joinsEquijoin simple join /inner join based on primary keys and foreign keys

You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions

Non-Equijoin don’t use = between is simplest process for non-equijoinOuter Join (+) placed on the side of the join that is deficient/missing in information

in/or operator prohibitedSelf Join

*If common column define qualifying ambiguous column names with table aliases upto 30 char Sql 1999ANSI SQL Join EQUIVALANCE ORACLE SQLCross same as Cartesian productNatural common column (same name and datatype) used ON clause Join on (col name) Equijoin Using clause join using Non-equijoin Left/Right/Full outer join Left outer join Outer join

• FULL OUTER JOIN TO VIEW all unmatched data from both tables. • Arbitary join condtn. On outer join And expression• Outer join can appear only one side of the expression• In OUTER JOIN Cannot use IN operator/cannot be linked with OR operator • You cannot link a condition that is involved in an outer join to another condition by using the OR operator.

Equivalence in Outer joins:SELECT last_name, department_name FROM employees e RIGHT OUTER JOIN departments d ON (e.department_id = d.department_id);

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Introduction to 9i SQL HandbookSame asSELECT e.last_name,d.department_name FROM employees e,departments d Where e.department_id(+) = d.department_id;SELECT last_name, department_name FROM employees e LEFT OUTER JOIN departments d ON (e.department_id = d.department_id);Same as SELECT e.last_name,d.department_name FROM employees e,departments d where e.department_id = d.department_id(+);

Isql*plus environment browser/internet/net environment• Temporary store values substitution variables & && define• substitution variables used anywhere in select statement• define variable CHAR type available for the session or until undefine• define x = a define x DEFINE X = "a" (CHAR)• define undefine x• Alias always in “ Alias name” {select ename [as] “employee Name” from emp;}• Isql*plus does not support validation check on user input• Altering dynamically headers and footers• Passing values to one sql to another• Verify on: force to show toggle between old & new substitution values• Verify off• Set to control current session• SET ECHO ON ECHO is system variable• Show echo/all to verify the set variables

Example of Define commandDEFINE _CONNECT_IDENTIFIER = "ORADB" (CHAR)DEFINE _SQLPLUS_RELEASE = "902000100" (CHAR)DEFINE _EDITOR = "Notepad" (CHAR)DEFINE _O_VERSION = "Oracle9i Enterprise Edition Release 9.2.0.1.0 – Production With the Partitioning, OLAP and Oracle Data Mining options JServer Release 9.2.0.1.0 - Production" (CHAR)DEFINE _O_RELEASE = "902000100" (CHAR)DEFINE SAL = "aa" (CHAR)DEFINE X = "a" (CHAR) */

Change column nameCOLUMN column_name HEADING EMPLOYEE_IDCOLUMN column_name HEADING SALARY FORMAT $9999COL[UMN]COL column_nameCOL column_name CLEARCLE[AR] COLCOL column_name NOPRINTCOL column_name PRINT

• Header ttitle text|off|on ttitle ‘salary|report’• Footer btitle text|off|on btitle ‘confidential’• Lengthy sql*plus command in script divide by hyphen(-)• ORACLE SERVER Uses POUND SIGN # in place of whole number exceeds or numeric represented by

alphanumeric (actual format)• BREAK TO DIVIDE ROWS INTO SECTIONS TO SUPRESS DUPLICATE VALUES• CLEAR BREAK• REM REMARK

Sample reportSET PAGESIZE 50SET LINESIZE 50SET FEEDBACK OFFTTITLE 'NIC REPORT'BTITLE 'CONFIDENTIAL.'BREAK ON DEPTNOCOLUMN DEPTNO HEADING Department|Name FORMAT 999

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Introduction to 9i SQL HandbookCOLUMN ENAME HEADING Employee|Name FORMAT A10COLUMN SAL HEADING Employee|Salary FORMAT $99,999.99SPOOL C:\SCRIPT1.LSTREM ‘it is the salary table from emp’SELECT DEPTNO,ENAME,SAL FROM EMP WHERE SAL<1500 GROUP BY DEPTNO,ENAME,SAL;SPOOL OFFHOST EDIT C:\SCRIPT1.LSTEXIT

DML statements (insert,update,delete,merge) form a logical unit of work TransactionDELETE:

• Delete all existing rows from a table, if no rows are deleted a message 0 rows deleted is returned.• Used by specifying where / ANY SUBQUERY or not specifying where clause.• DELETE FROM EMP WHERE DEPTNO = 10; DELETE FROM EMP;• If table is parent of referential integrity constraint, Cannot DELETE must disable the constraint before DELETE

Insert : • sub query in where clause WITH CHECK OPTION on which column must be in values(list)• DEFAULT keyword to identify a default column value use only in insert or update command• No default value oracle sets the column null

Merge:• Avoids separate value updates• Increase performance and ease of use• Useful in Data warehousing applications• Need both insert or update privilege• Alternative approach to use PL/SQL blocks or loops

Sample MergeMERGE INTO new_employees cUSING employees e ON (c.employee_id = e.employee_id)WHEN MATCHED THENUPDATE SET c.name = e.first_name ||’,’|| e.last_nameWHEN NOT MATCHED THENINSERT VALUES(e.employee_id, e.first_name ||’,‘||e.last_name);

Transaction • Ensures data consistency based on Transactions (user process failure/system failure)• consists one of 1. DML STATEMENTS 2. only one DDL 3.only one DCL statements• begin when first DML executes• Commit/rollback• DDL or DCL statements (automatic commit)• Exits iSQL*Plus/abnormal termination of iSQL*Plus• System Crashes entire transaction rolled back• Transaction Control (Commit/rollback/savepoint savepoint_name /rollback to savepoint_name ) • Autocommit [on|off]• Commit/rollback Ensures data consistency/preview data changes/group logically related operations• Creating second savepoint with same name earlier savepoint is deleted

Example of Transactional statements:CREATE table new_emp ( employee_id NUMBER, name VARCHAR2(30));INSERT INTO new_emp SELECT employee_id , last_name from employees;Savepoint s1;UPDATE new_emp set name = UPPER(name);Savepoint s2;Delete from new_emp;Rollback to s2;Delete from new_emp where employee_id =180;UPDATE new_emp set name = 'James';

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Introduction to 9i SQL HandbookRollback to s2;UPDATE new_emp set name = 'James' WHERE employee_id =180;Rollback;At the end of this transaction, you have no rows in the table.Before Commit /Rollback

• Affect the database buffer so Previous state of data can be recovered• Current user can review results of DML by querying• Other user cannot view the results of DML by Current user• Affected row rows are locked

After Commit• Data changes written to database• Previous state of data lost permanently• All user view the results• Locks are released• Savepoint are erased

After Rollback • Previous state of data recovered• Data changes are undone• All pending transactions are deleted.• Locks are released

Statement level rollback• Single DML fails, only that statement rolled back• Oracle server issues an implicit commit or savepoint before or after DDL

Read Consistency1. An automatic implementation2. insert,update,delete issued oracle server takes a copy of unchanged data in undo segment3. All users except the issuer view data from rollback segment as snapshot4. After commit space occupied by undo segment is freed for reuse5. Oracle server Guarantees a consistent view of data at all times6. Changes made by one user do not conflict Changes made by other user7. Read operation(select)/write operation (insert,update,delete)8. Readers don’t wait for writers/Writers don’t wait for readers

Locks:• Prevent destructive interaction between concurrent transactions• Require no user action• Use automatically the lowest level of restrictiveness• Held when transaction in progress• Lock Two types Explicit & Implicit• Implicit locking occurs for all SQL statements except SELECT

o Exclusive: locks out other userso Share: Allows other user to accesso High level of data concurrencyo DML: table share row exclusiveo Queries: no locko DDL: protects object definitionso Locks held until commit or rollback

• Explicit locking User puts manual lock

Database Objects: Table Basic unit of storage; rows and columns• Table can be created anytime, online structure modification no need to specify memory size of table, size

ultimately defined by amount of space allocated to the databaseNaming Rules:

o Must be 1-30 characters long. Object names or Qualifier are case insensitive EMP or emp sameo Should not be an Oracle Server reserved word.o Must contain only A-Z, a-z, 0-9, _, $, and #.o Must begin with a letter.(use descriptive name)

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Introduction to 9i SQL Handbooko Must not a duplicate name of another object owned by same user.

• Before construct a table see 1. Create table privilege 2. Storage area• Input: Table name, column data type, name and size.• Create DDL statement: to store structure, immediate effect on database, record information in data-

dictionary.• Create table DDL command Auto commit happens

Schema is collection of objects, the logical structures that directly refer to data in a database.Schema Objects: TABLES, VIEWS, SYNONYMS, SEQUENCES, STORED PROCEDURES, INDEXES, CLUSTERS, DATABASE LINKSSchema is owned by user and has the same name as user name, tables belonging to other users not in current user schema, to access use user name as prefix user.Obj_name

• Default value for a column during an insert as Hire_date DATE DEFAULT SYSDATE User_name varchar2(10) DEFAULT USER

• Default value accepts Literal values, expressions, SQL functions [legal values]• Default value does not accept another column’s name or a pseudo column [illegal values]• Default data type must match column data type

Tables in Oracle databaseUser table collections of tables created and maintained by user/ contain user informationData dictionary collections of tables created and maintained by Oracle server/ contain database information

Data dictionary tables’ owner is SYS userData dictionary information: Names of Oracle server users, privileges granted, database object names,

Table Constraints, Auditing information4 categories of Data dictionary views (with distinct prefix)USER_ views contain user’s object informationALL_ views contain all tables (object & relational) information accessible to userDBA_ restricted views accessible by DBA role granted usersV$ views contain dynamic performance views, Database server performance, memory, lockingImp query: select table_name from USER_TABLES; | select distinct object_type from USER_OBJECTS;select * from USER_catalog; USER_catalog=synonym=CAT | select distinct type from all_source;Create table using subquery:

• Column definitions can contain only column name and default value• Integrity rules are not passed onto new table.• If in subquery any function or calculation used as sal*10 or upper (name) then a new column alias must

be used.Add a new column ALTER TABLE table_name ADD (col_name data_type(size));

• Add or modify but can’t specify where the column is to appear (as last column)• If table already contains rows then added column is initially null for all the rows

Modify an existing column ALTER TABLE table_name modify (col_name data_type(size));• Change data type, size, and A change to the DEFAULT value affects only subsequent insertions to table.• Increase width of numeric or character/ precision of a numeric column• Decrease width of column if column contains only null values or has no rows• Change data type if column contains only null• Data type change possible for: CHAR TO VARCHAR2 or VARCHAR2 TO CHAR if column contains only null

values or the size is same.Drop a column ALTER TABLE table_name DROP COLUMN col_name; (from Oracle 8i)

• Column may/may not contain data• Only one column dropped at a time• Must have one column remaining after alter• Dropped column cant be recovered.

UNUSED COLUMN IN TABLE• To mark a column as unused so that it can be dropped when system resource is lower.• Treated as they are dropped even they exists.• If column marked as unused user has no access to those columns.• Both in desc table_name and Select * from table_name command user cannot view those used column.• User can also add a new column using same name of unused column

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Introduction to 9i SQL Handbook• Unused column information stored in USER_UNUSED_COL_TABS dictionary view.• UNUSED statements complete a transaction

ALTER TABLE TABLE_NAME SET UNUSED (COLUMN_NAME);ALTER TABLE TABLE_NAME SET UNUSED COLUMN COLUMN_NAME;ALTER TABLE TABLE_NAME DROP UNUSED COLUMNS; (If table contains no UNUSED columns, statement returns with no error)DROP TABLE: DROP TABLE TABLE_NAME

• All data & structure is deleted, All Indexes associated with it are dropped, view and synonym remain but invalid.

• Any pending transactions are committed, as DROP DDL command Auto commit happens, can’t rollback.• Creator/Owner user or high level privileged user (DROP ANY TABLE) can DROP table.• Rename of Object (TABLES, VIEWS, SYNONYMS, SEQUENCES)• RENAME old_table_name to new_table_name; // Owner user can do it. DDL command Auto commit

happens.Truncate: TRUNCATE TABLE TABLE_NAME

• Remove all rows from a table• Owner user or high level privileged user (DELETE TABLE) can DROP table.• DDL command Auto commit happens, CANNOT ROLLBACK• Release storage space used by that table• If table is parent of referential integrity constraint, Cannot truncate, must disable the constraint before TRUNCATE.

The Main Difference between DELETE & TRUNCATE are:-1. DELETE - is a DML Command & TRUNCATE - is a DDL Command2. After DELETE - can rollback the Records & After TRUNATE - cannot rollback the records3. In DELETE Command you can give the conditions in WHERE Clause & In TRUNCATE you cannot give conditions 4. After using DELETE Command the memory will be occupied till the user does not give ROLLBACK or COMMIT & after

using TRUNCATE Command the memory released immediately.5. TRUNCATE Command is faster than DELETE Command because it does not fire the delete triggers of the table.

COMMENTS:• Add comment up to 2000 bytes about a column, table, view or snapshot• Comment can be viewed from following data dictionary views:• ALL_COL_COMMENTS USER_COL_COMMENTS ALL_TAB_COMMENTS USER_TAB_COMMENTS

• Add Comment: COMMENT ON TABLE table_name is ‘Table Information’;• COMMENT ON COLUMN table_name.column_name is ‘Column Information’;• Drop Comment (empty string): COMMENT ON TABLE table_name is ‘ ’;

Constraints• Oracle server uses constraints to prevent invalid data entry into tables. • Constraints must be satisfied for the operation to succeed. • Enforce rules at table and view level. (Row insertion, deletion, updating). • To prevent DELETION OF A TABLE if there are dependencies. • Provide rules for Oracle Tools (e.g. Oracle Developer).• Constraints stored in data dictionary (USER_CONSTRAINTS).• Provide a meaningful name follow standard object-naming rules.• If not specify name Oracle server generates a name as SYS_Cn [n is integer to make the name unique]• Create a constraint at the same time or after of table creation.• Define a Constraint in table or column level.• Create table schema.table_name (column_name data type(size) [default expr] [column_constraint], …,

[table_constraint]);• column_constraint level: reference a single column defined within a specification for owning column,

define any type of integrity constraint. column [constraint constraint_name] constraint_typee.g. create table t1(Emp_id number(6) constraint emp_id_uk unique, ename char(10) not null);here constraint for Emp_id is user named & constraint for ename system named table_constraint level: reference one or more columns defined separately from definitions of column, any type of integrity constraint except NOT NULL. [constraint constraint_name] constraint_type (column_name)e.g. create table t1(Emp_id number(6), ename char(10) not null, constraint emp_id_uk unique(Emp_id));

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Introduction to 9i SQL Handbook

• NOT NULL can be specified only in column level not in table level• UNIQUE every value in a column must be unique• Single column (set of columns) uses this constraint is called unique key if two or more column comprises

this groups of columns is called composite unique key.• UNIQUE can be specified in column or table level. Composite unique key specified table level• Unique Constraints allow the input of nulls because nulls are not considered equal to anything. So

user also defines NOT NULL to prevent null acceptance • Oracle server enforces UNIQUE constraints by implicitly creating a unique index on the unique key

column or columns.• Primary key constraint is a column or sets of columns, only one primary key is defined.• Enforce uniqueness for column or column combination but don’t accept null values.• Primary key can be specified in column or table level. Composite Primary key specified table level• Table contains only one primary key constraint but several unique constraints.• A UNIQUE index is automatically created for a Primary key column.• Foreign Key referential integrity designates a column or combination of columns & establishes a

relationship between a primary key or a unique key in same or different table.• Foreign Key must match an existing value in the parent table or be NULL.• Foreign Key are based on data values and are purely logical, not physical, pointers.• Foreign key can be specified in column or table level. Composite Foreign key specified table level• create table t1(Emp_id number(6) constraint emp_id_fk references dept (Emp_id));• create table t1(Emp_id number(6), constraint emp_id_fk Foreign key (Emp_id) references

dept (Emp_id));• FOREIGN KEY: Defines the column in the child table at the table constraint level• REFERENCES: Identifies the table and column in the parent table• ON DELETE CASCADE: deletes the dependent rows in the child table when a row in parent table

is deleted• ON DELETE SET NULL: converts dependent foreign key values to null when parent table is deleted• Default behavior of Foreign Key is called Restrict rule.• CHECK is a condition that each row must satisfy (both column or table level)• References to CURRVAL, NEXTVAL, LEVEL, ROWNUM pseudocolumns• Calls to SYSDATE, UID, USER AND USERENV functions• Queries that refer to other values in other rows• Single column can have multiple CHECK Constraints which refer to the column in its definition.• No limit to the no. of CHECK Constraints which user can define on a column.• salary number(8) check (salary>0) | city varchar2(10), constraint emp_city_ck check (city

in (‘Kol’,’Delhi’,’Mumbai’))• Add or Drop a constraint but can’t modify its structure• ALTER TABLE ADD constraint constraint_name constraint_type (COLUMN_NAME[s]);• ALTER TABLE EMP ADD CONSTRAINT EMP_MANAGER_FK FOREIGN KEY (MGRID) REFERENCES

EMP(EMPID);• If user doesn’t specify constraint_name system itself generate a name.• Change existing column to not null constraint if the table is empty or column has value for every row.• Add a NOT NULL constraint only by using MODIFY clause of ALTER TABLE statement

• ALTER TABLE T1 MODIFY NAME CONSTRAINT NAME_NN NOT NULL;• ALTER TABLE TABLE_NAME DROP CONSTRAINT constraint_name• CASCADE option used to drop dependent constraints (referential integrity to PK or UK).• CASCADE CONSTRAINTS used along DROP COLUMN clause/to drop multicolumn constraints.• ALTER TABLE TABLE_NAME DROP primary key|unique(column)| CONSTRAINT constraint_name [cascade];

• ALTER TABLE TABLE_NAME DROP (column_name) CASCADE CONSTRAINTS;• After dropping a constraint it no longer available by Oracle server data dictionary

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Introduction to 9i SQL Handbook• DISABLE Clause to deactivate an integrity constraint/ apply cascade to disable dependent constraint• Alter table table_name disable constraint constraint_name cascade;• Disabling a unique or primary key constraint removes the unique index• Enable Clause to activate an integrity constraint used both in CREATE TABLE or ALTER TABLE statement• After enabling constraint, data must fit to it otherwise report error.• Enabling a unique or primary key constraint create the unique index• Enabling a primary key constraint disabled with CASCADE option does not enable foreign keys dependent

on this primary key.• Data dictionary views to view constraints for user given or system-assigned name• Select CONSTRAINT_name, CONSTRAINT_type, search_condition from USER_CONSTRAINTS;

o Here C CHECK, P PRIMARY KEY, RREFERENTIAL INTEGRITY, UUNIQUE KEYo NOT NULL also CHECK type CONSTRAINT.

• Select CONSTRAINT_name, column_name from USER_CONS_COLUMNS;

Database Objects: View logically represents subsets of data from one or more tables• A view itself contains no data but a window through which data from another table can viewed or

changed.• Tables are called base table. View is stored as SELECT statement in data dictionary.• Use views to restrict data access, to make complex queries easy, to provide data independence for ad

hoc users and application programs, to present different views of the sane data according particular criteria.

• Simple View derived data from one table, Contains no functions or groups of data, allow DML operations.

• Complex View derived data from many tables, Contains functions or groups of data, not always allow performing DML operations (Select, insert, delete, update) through view.

• Cannot remove a row if view contains: o Group Functions, Group by clause, distinct clause, ROWNUM keyword

• Cannot modify/update data if view contains: o Group Functions, Group by clause, distinct clause, ROWNUM keyword, column

defined by expressions (as sal*12)

Cannot add data if view contains: o Group Functions, Group by clause, distinct clause, ROWNUM keyword, column

defined by expressions (as sal*12), not null columns without default values in base tables not selected by the view

• Embed a subquery (containing complex select statement) within create view statement.

CREATE OR REPLACE FORCE [NOFORCE by default] VIEW EMPVU80(EMPLOYEE_ID80,LAST_NAME80,SALARY80) //(Alias)AS SELECT EMPLOYEE_ID,LAST_NAME,SALARY FROM emp WHERE employee_ID=1WITH CHECK OPTION CONSTRAINT constraint_nameWITH READ ONLY CONSTRAINT constraint_name;

• Use or replace to recreate the views with new values from table• If no column exists in table but used in subquery user uses FORCE command result: • “Warning: View created with compilation errors.” By default NOFORCE used as base tables exist.

Alias column names must match the number of expressions selected by the view and aliases are listed in the same order as columns in subquery.WITH CHECK OPTION specifies that only rows accessible to the view can be inserted or updated. Acts upon where clause, to perform referential integrity checks through views, enforces constraints in database level. Data validation check, if user want to modify employee_ID=2 it results error.WITH READ ONLY to deny DML operations, if DML operations performed results Oracle server error “virtual column not allowed here”

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Introduction to 9i SQL Handbook• Complex views contains group functions, joins to display values from two tables• Remove/Drop view without data loss because view is based on underlying tables in database• DROP VIEW view_name; remove view definitions from database.• Creator or user with DROP ANY VIEW privilege can drop a view• Inline view is a subquery with an alias or correlation name use within SQL statement• Placing a subquery in the from clause and giving the subquery an alias• Subquery defines a data source referred in main query.• E.g. Select a.last_name, a.salary, b.maxsal from employees a, (select department_id, max(salary)

maxsal from employees group by department_id) b where a.department_id = b.department_id;• Top-n analysis to display n top-most or n bottom-most records from a table based on condition• Top-n queries use a consistent nested query structure (High level structure) as• A subquery/ outer query or inline view to generate sorted list of data and ORDER BY clause• Outer query to limit no. of rows in final result set including ROWNUM pseudo column assigns a sequential

value starting from 1 to each of the rows returned from the subquery• An Outer where clause specifies the n rows to be returned, must use < or <= operator. • E.g1. select last_name,salary, rownum from (select last_name,salary from employees order by salary

desc) where rownum<=&n;• E.g2. SELECT LAST_NAME,SALARY FROM EMPLOYEES WHERE SALARY = (SELECT MIN(SALARY) FROM

(SELECT DISTINCT(SALARY) FROM EMPLOYEES ORDER BY SALARY DESC) WHERE ROWNUM <=&X);• Data dictionary view: user_views select VIEW_NAME,TEXT from user_views;• SET LONG 1000 OR Select VIEW_NAME,TEXT from user_views ORDER BY LINE;

• You want to look at the definition of the EMP_DEPT_VU view?• Query the USER_VIEWS data dictionary view to search for the EMP_DEPT_VU view

Database Objects: Sequence Numeric value generator• Generate unique sequential numbers• Sharable object for multiple tables as created independently of tables.• used to create primary key value, belong to a specific schema• time saving object as reduce or replaces application code needed to write a sequence generating routine• speeds up efficiency of accessing sequence values when cached in memory• incremented or decremented by internal oracle routine• caching sequence values in memory gives faster execution• gaps created when rollback occurs, system crashes, sequence used in another table,

CREATE SEQUENCE sequence_EXincrement by 10Start with 100Maxvalue 1000Nocycle | CYCLENocache | CACHE 25CREATE SEQUENCE sequence_nameincrement by aStart with bMaxvalue c |nomaxvalue [10^27 ascending sequence -1 descending sequence]Minvalue d |nominvalue [1 ascending sequence – (10^26) descending sequence]Nocycle | Cycle [continue to generate values after reaching its max or min value]Cache e | nocache [oracle server preallocates and keep values in memory default 20 values]

• If SEQUENCE used in primary key don’t use CYCLE option • Do not use MAXVALUE AND MINVALUE AT SAME TIME. • CONFIRM SEQUENCE FROM user_objects then user_sequences DATA DICTIONARY TABLE

select SEQUENCE_NAME,MIN_VALUE, MAX_VALUE, INCREMENT_BY, CYCLE_FLAG, CACHE_SIZE, LAST_NUMBER from user_sequences;

• LAST_NUMBER column displays next available sequence no if Nocache is specifiedNEXTVAL & CURRVAL are pseudo columns

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Introduction to 9i SQL Handbooko NEXTVAL RETURNS next available sequence value, different/unique for each time even for

different users by actually retrieving the value from the sequence.o CURRVAL obtains current available sequence value, without affecting the further values to be

generated from the sequence.o NEXTVAL must be issued for a sequence 1st time before CURRVAL contains a value.

• select SEQUENCE_EX.NEXTVAL from dual;• select SEQUENCE_EX.CURRVAL from dual;• Usage in : select list of a select statement not a part of subquery

o select list of a subquery in an INSERT statemento values clause in an INSERT statemento set clause of an update statement

• Not Usage in : select list of a viewo Select statement with distinct keyword, group by, having, order by clauseo subquery in SELECT, UPDATE, DELETE statemento DEFAULT expression in create table or alter table

• Insert into dept(deptno,dname) values (dept_seq.nextval,’AMC’);• Modify sequence only increment value, maxvalue, minvalue, cycle or cache option.• To modify user must have ALTER privilege• Only future sequence numbers are affected• If Maxvalue limit is reached modify maxval to continue, cant modify start with once created.• Then sequence dropped and re-created to restart sequence at a different number• Validation like maxvalue can’t less than current value performed• Remove a sequence user must have DROP SEQUENCE privilege• DROP SEQUENCE sequence_name; //no longer be referenced upon deletion

Database Objects: Index Improve performance of some queries• Index is a schema object, used and maintained automatically by oracle server to speed up the retrieval of

rows by using a pointer• Can reduce disk I/O by using rapid path access method to locate data quickly• Is logically and physically independent of the table it indexes• Can drop any time without affecting the base tables or indexes • Direct and fast access to rows, without index on a column a full table scan occurs• Created explicitly or automatically; after creation no direct activity required by user• Automatically unique index created when primary key or unique constraints are used• Name of index same as constraint name• User explicitly creates non-unique index on column to fast access to rows• CREATE INDEX index_name ON table_name (column_name1,…, column_nameN);• Function base index based on expression (table columns, constants, SQL function, user-defined

functions)• CREATE INDEX index_name ON table_name UPPER(column_name1) ; //case-insensitive search• ORACLE SERVER TREATS INDEXES WITH COLUMNS MARKED desc AS Function base index• More indexes mean more effort to oracle server to update those indexes, because when DML statement

committed to table index must be updated.When to create index:• When column contains wide range of values, large no. of null values, one or more columns are frequently

together in a WHERE or JOIN condition, large table and most of queries uses less than 2-4% of the rows.• Better approach to make a column applied unique constraintWhen not to create index:• Table is small, updated frequently, columns are not often used in where or JOIN clause, most of queries

uses more than 2-4% of the rows, indexed columns are referenced as apart of an expression. Data dictionary views: USER_INDEXES (INDEX_NAME, INDEX_TYPE, TABLE_NAME, UNIQUENESS)

USER_IND_COLUMNS (INDEX_NAME, TABLE_NAME, COLUMN_NAME, COLUMN_POSITION)• Cannot modify an index must drop then recreate it.• Remove AN INDEX user must have DROP ANY INDEX privilege• DROP INDEX index_name; //to remove index definition from data dictionary

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Introduction to 9i SQL Handbook• If any table is dropped dependent indexes , constraints also dropped, but vies and sequences

remain.Database Objects: Synonym Alternative names to objects

• Simplify access to objects by creating synonym• Ease referring to a table owned by another user• Shorten lengthy object names• Object cannot be contained in a package• Public synonym accessible to all users, CREATES ONLY BY DATABASE ADMINISTRATOR• Private synonym must be distinct from all other objects owned by same user• CREATE SYNONYM synonym_name FOR object_name;• CREATE PUBLIC SYNONYM synonym_name FOR user. object_name;• DATABASE ADMINISTRATOR only drop public synonym • DROP [PUBLIC] SYNONYM synonym_name;• View public synonyms from all_synonyms and user created synonyms from user_synonyms tables.

SPECIAL Cases• DBA CREATE PUBLIC SYNONYM xyz FOR userA.object_name;• userB has a user object named xyz.• userB queries select * from xyz;• result from userB.xyz object not from public synonym;

DATABASE LINKSCONN SYS/SYS AS SYSDBASQL> CREATE PUBLIC DATABASE LINK HQ.ACME.COM USING 'ORADB'; //ORADB SERVICE NAMEDatabase link created. TABLE_NAME in DICTIONARY 1.ALL_DB_LINKS 2.DBA_DB_LINKS 3.USER_DB_LINKSSQL> SELECT * FROM ALL_DB_LINKS;SQL>SELECT * FROM DBA_DB_LINKS;OWNER DB_LINK ------------------------------ ----------------------------------PUBLIC HQ.ACME.COM SQL> CONN HR/HRConnected.SQL> SELECT * FROM EMPLOYEES@HQ.ACME.COM;

Controlling user access• Oracle server database security: control database access• Give access to specific objects• Confirm given and received privileges with the data dictionary• Create synonyms for database objects• System security: use of database at system level username password disk space allocation system

operations• Data Security: access and use of database objects actions taken by user on those database objects• Privilege is the right to execute particular SQL statement [DBA is high-level user ability to grant user

access to database and its objects

System Privilege: gaining access to database• More than 100 Privileges available for users and roles• Only DBA provides System Privileges CREATE USER, DROP USER, DROP ANY TABLE, BACKUP

ANY TABLE, SELECT ANY TABLE, CREATE ANY TABLE• DBA can create user as CREATE USER user_name IDENTIFIED BY password• Change password by user: alter user user_name identified by new_password; or command

password• After creating user, user has no privilege or can’t action on database• GRANT user certain privilege: GRANT privilege_name to user_name|role_name|PUBLIC;• SOME privileges name: CREATE SESSION|TABLE|VIEW|SEQUENCE|PROCEDURE

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Introduction to 9i SQL Handbook• Public means grant privilege to all database user• Users also be given the privilege to grant additional privilege to other user or to roles, role is named

group of related privileges that can be granted to the user• Is a method to make easier revoke or maintain privileges • Only DBA can Create role as CREATE ROLE role_name;• Grant privilege_name[s] to role_name; Grant role_name to user _name[s];• A user can have access to several roles, and several users can be assigned the same role. • Granted current system privilege can be viewed from SESSION_PRIVS data dictionary view

Object Privilege: To Manipulate content of database objects• Perform particular action on a specific TABLE|VIEW|SEQUENCE|PROCEDURE• Some Object Privileges: ALTER|DELETE|EXECUTE|INDEX|INSERT|REFERENCES|SELECT|UPDATE• TABLE/SYNONYM: ALTER|DELETE|INDEX|INSERT|REFERENCES|SELECT|UPDATE• VIEW: DELETE|INSERT|REFERENCES|SELECT|UPDATE• SEQUENCE: ALTER|SELECT• PROCEDURE: EXECUTE• Owner of an object has all privilege or all object in it’s schema, can give specific privilege on that object• GRANT object_privilege(s)|ALL on object_name TO user_name(s)|role_name(s)|PUBLIC

[with grant option];• with grant option It allows the grantee to grant object privileges to other users and roles. • E.g. GRANT SELECT ON EMP TO SCOTT; EMP is a HR user’s table

Now scott access the emp table as select * from HR.EMP;DBA generally allocate System privileges and User grants object privilegesGranted Object privileges can be viewed from following data dictionary viewUSER_COL_PRIVS_MADEUSER_COL_PRIVS_RECDUSER_ROLE_PRIVSUSER_SYS_PRIVSUSER_TAB_PRIVSUSER_TAB_PRIVS_MADEUSER_TAB_PRIVS_RECDROLE_ROLE_PRIVSROLE_SYS_PRIVSROLE_TAB_PRIVSRevoke privilegeREVOKE { privilege [,privilege…]|ALL} on object from {user[,user…]|role|PUBLIC}[CASCADE CONSTRAINTS];CASCADE CONSTRAINTS is required to remove any referential integrity constraints made to object by means of the REFERENCES privilege Revoke select, insert On dept from scott;

Data typesROWID: A hexadecimal string representing the unique address of a row in its table.Which three are DATETIME data types that can be used when specifying column definitions?

1. TIMESTAMP2. INTERVAL DAY TO SECOND3. INTERVAL YEAR TO MONTH

Statements:Data Retrieval SELECTDML INSERT, UPDATE, MERGE, DELETEDDL CREATE, ALTER, DROP, RENAME, TRUNCATETransaction Control COMMIT, ROLLBACK, SAVEPOINTDCL GRANT, REVOKE

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Introduction to 9i SQL Handbook

DELETE employee_id, salary, job_id FROM employees WHERE dept_id = 90;DELETE statement fail because user cannot specify column names in the DELETE clause of the DELETE statement.DELETE FROM employees WHERE dept_id = 90; if no rows are deleted a message 0 rows deleted is returned.

Self Join:Which statement lists the ID, name, and salary of the employee, and the ID and name of theemployee's manager, for all the employees who have a manager and earn more than 4000?

SELECT e.employee_id "Emp_id", e.last_name "Employee", e.salary,m.employee_id "Manager_id", m.last_name "Manager"FROM employees e, employees mWHERE e.manager_id = m.employee_idAND e.salary > 4000;Which statement shows the department ID, minimum salary, and maximum salary paid in that department, only of the minimum salary is less then 3000 and the maximum salary is more than 7000?SELECT department_id, MIN(salary), MAX(salary) FROM employees GROUP BY department_id HAVING MIN(salary) < 3000 aND MAX(salary) >7000; ORSELECT department_id, MIN(salary), MAX(salary) FROM employees HAVING MIN(salary) < 3000 aND MAX(salary) >7000 GROUP BY department_id ;RESULT:DEPARTMENT_ID MIN(SALARY) MAX(SALARY)------------- ----------- ----------- 30 2500 11000 50 2100 8200SELECT department_id, MIN(salary), MAX(salary) FROM employees GROUP BY department_id, salaryHAVING MIN(salary) < 3000 AND MAX(salary) >7000;no rows selectedselect &1,&2 from &3 where ename = '&4';SELECT ROUND(456.953,-1) FROM DUAL; 460 SELECT TRUNC (456.953,-1) FROM DUAL; 450SELECT ROUND(456.953,-2) FROM DUAL; 500 SELECT TRUNC (456.953,-2) FROM DUAL; 400SELECT ROUND(456.953,-3) FROM DUAL; 0 SELECT TRUNC (456.953,-3) FROM DUAL; 0SUBSTR(‘RAKESH’,-1 = SUBSTR(‘RAKESH’,-1,1) H

Subquery used in1. From clause of a select statement2. Where clause of a select statement3. Update clause of a set statement4. Values clause of a insert statementIT WORKS:SELECT ENAME,SAL FROM EMP WHERE SAL IN (SELECT MAX(SAL) FROM EMP GROUP BY DEPTNO);

Examine the data in the EMPLOYEES and DEPARTMENTS tables.You want to retrieve all employees' last names, along with their manager's last namesand their department names. Which query would you use?SELECT e.last_name, m.last_name, department_nameFROM employees eLEFT OUTER JOIN employees m on ( e.managaer_id = m.employee_id)LEFT OUTER JOIN departments d ON (e.department_id = d.department_id);

SQL> SELECT SUM(SAL), MAX(SAL) FROM EMP WHERE HIREDATE > '17-DEC-80'; SUM(SAL) MAX(SAL)---------- ---------- 28225 5000SQL> SELECT SUM(SAL), MAX(SAL) FROM EMP WHERE HIREDATE BETWEEN '17-DEC-80' AND '17-DEC-83'; SUM(SAL) MAX(SAL)---------- ----------

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Introduction to 9i SQL Handbook 24925 5000

SELECT D.DEPARTMENT_NAME FROM EMPLOYEES E JOIN DEPARTMENTS DON (E.DEPARTMENT_ID = D.DEPARTMENT_ID)WHERE E.JOB_ID LIKE 'SA_REP'GROUP BY DEPARTMENT_NAMEHAVING COUNT(EMPLOYEE_ID)>5;

SELECT TEXT FROM USER_SOURCE where NAME LIKE 'ADDIT' ORDER BY LINE;

Inline viewselect a.ename,a.sal,a.deptno,b.maxsal from emp a,(select deptno, max(sal) maxsal from emp group by emp.deptno)bwhere a.deptno = b.deptnoand a.sal<b.maxsal

1 CLARK 2695.00 10 50002 MILLER 1300.00 10 50003 SMITH 800.00 20 30004 ADAMS 1100.00 20 30005 JONES 2975.00 20 30006 ALLEN 1600.00 30 28507 MARTIN 1250.00 30 2850

TOP N Analysis

select rownum as rank,ename , salfrom (select ename,sal from emp order by sal desc)where rownum<=31 1 KING 5000.002 2 SCOTT 3000.003 3 FORD 3000.00

select ename,sal, rownum from (select ename,sal from emp order by sal desc) where rownum<=&n; --4

1 KING 5000.00 12 SCOTT 3000.00 23 FORD 3000.00 34 JONES 2975.00 4

SELECT ename,SAL FROM EMP WHERE SAL = (SELECT MIN(SAL) FROM (SELECT DISTINCT(SAL) FROM EMP ORDER BY SAL DESC) WHERE ROWNUM <=&X); -- 21 SCOTT 3000.002 FORD 3000.00

--Inline viewselect a.ename,a.sal,a.deptno,b.maxsal from emp a,(select deptno, max(sal) maxsal from emp group by emp.deptno)bwhere a.deptno = b.deptnoand a.sal<b.maxsal;

--TOP N Analysis

select rownum as rank,ename , salfrom (select ename,sal from emp order by sal desc)where rownum<=3;select ename,sal, rownum from (select ename,sal from emp order by sal desc) where rownum<=&n; --4

SELECT ename,SAL FROM EMP WHERE SAL = (SELECT MIN(SAL) FROM (SELECT DISTINCT(SAL) FROM EMP ORDER BY SAL DESC) WHERE ROWNUM <=&X); -- 2

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Introduction to 9i SQL Handbook

SELECT MIN(SAL) "2nd Highest" FROM (SELECT DISTINCT(SAL) FROM EMPORDER BY SAL DESC) WHERE ROWNUM <=2;SELECT MAX(SAL) "2nd lowest" FROM (SELECT DISTINCT(SAL) FROM EMPORDER BY SAL ASC) WHERE ROWNUM <=2;

--connect by prior

select sal from empconnect by prior sal<salgroup by salselect max(sal) "2nd Highest" from empwhere level = 2connect by prior sal>salselect min(sal) "2nd Lowest" from empwhere level = 2connect by prior sal<salselect level, max(sal) "2nd Highest" from empwhere level=2 connect by prior sal > salgroup by level

------------------------------CONNECT BY PRIOR--A condition that identifies the relationship between parent rows and child rows of the hierarchy

CONNECT BY <child_value> = <parent_value>--conn hr/hr

SELECT employee_id, last_name, manager_idFROM employeesCONNECT BY PRIOR employee_id = manager_id; --START WITH--Specifies a condition that identifies the row(s) to be used as the root(s) of a hierarchical query

START WITH (column_name) = <value>--conn hr/hr

SELECT last_name, employee_id, manager_id, LEVELFROM employees

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Introduction to 9i SQL HandbookSTART WITH employee_id = 100CONNECT BY PRIOR employee_id = manager_id;SELECT last_name, employee_id, manager_id, LEVELFROM employeesSTART WITH employee_id = 101CONNECT BY PRIOR employee_id = manager_id;set pagesize 0col last_name format a30

SELECT LEVEL, LPAD(' ', LEVEL*3) || LAST_NAME AS LAST_NAMEFROM employeesSTART WITH employee_id = 100CONNECT BY PRIOR employee_id = manager_id;set pagesize 20 --ORDER SIBLINGS BY--SIBLINGS BY preserves any ordering specified in the hierarchical query clause and then applies the order_by_clause to the siblings of the hierarchy ORDER SIBLINGS BY (column_name)--conn hr/hr

SELECT last_name, employee_id, manager_id, LEVELFROM employeesSTART WITH employee_id = 100CONNECT BY PRIOR employee_id = manager_idORDER SIBLINGS BY last_name; --CONNECT_BY_ROOT--CONNECT_BY_ROOT is a unary operator that is valid only in hierarchical queries. When you qualify a column with this operator, Oracle returns the column value using data from the root row.

--Cannot be specified with the START WITH or CONNECT BY condition. The following example returns the last name of each employee in department 110, each manager above that employee in the hierarchy, the number of levels between manager and employee, and the path between the two:--conn hr/hr

set linesize 121col emp format a20col mgr format a20

SELECT "Name", SUM(salary) "Total_Salary"FROM ( SELECT CONNECT_BY_ROOT last_name "Name", salary FROM employees WHERE department_id = 110 CONNECT BY PRIOR employee_id = manager_id)GROUP BY "Name";-- Thanks Colin for the correction --CONNECT_BY_ISCYCLE Pseudocolumn--The CONNECT_BY_ISCYCLE pseudocolumn returns 1 if the current row has a child which is also its ancestor. Otherwise it returns 0--conn hr/hr

UPDATE employees SET manager_id = 145WHERE employee_id = 100;set linesize 121col path format a50

SELECT last_name, LEVEL, SYS_CONNECT_BY_PATH(last_name, '/') "Path"FROM employeesWHERE LEVEL <= 3 AND department_id = 80START WITH last_name = 'King'CONNECT BY PRIOR employee_id = manager_id AND LEVEL <= 4;--ERROR:--ORA-01436: CONNECT BY loop in user data

SELECT last_name, CONNECT_BY_ISCYCLE "Cycle", LEVEL, SYS_CONNECT_BY_PATH(last_name, '/') "Path"FROM employeesWHERE LEVEL <= 3 AND department_id = 80START WITH last_name = 'King'CONNECT BY NOCYCLE PRIOR employee_id = manager_idAND LEVEL <= 4;

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Introduction to 9i SQL Handbook

ROLLBACK; --CONNECT_BY_ISLEAF Pseudocolumn--The CONNECT_BY_ISLEAF pseudocolumn returns 1 if the current row is a leaf of the tree defined by the CONNECT BY condition. Otherwise it returns 0. This information indicates whether a given row can be further expanded to show more of the hierarchy.--conn hr/hr

SELECT last_name "Employee", CONNECT_BY_ISLEAF "IsLeaf",LEVEL, SYS_CONNECT_BY_PATH(last_name, '/') "Path"FROM employeesWHERE level <= 3AND department_id = 80START WITH last_name = 'King'CONNECT BY PRIOR employee_id = manager_idAND LEVEL <= 4; --LEVEL Pseudocolumn--For each row returned by a hierarchical query, the LEVEL pseudocolumn returns 1 for a root row, 2 for a child of a root, and so on--conn hr/hr

SELECT employee_id, last_name, manager_id, LEVELFROM employeesCONNECT BY PRIOR employee_id = manager_id;SELECT LPAD(' ',2*(LEVEL-1)) || last_name ORG_CHART,employee_id, manager_id, job_idFROM employeesSTART WITH job_id = 'AD_VP'CONNECT BY PRIOR employee_id = manager_id; --SYS_CONNECT_BY_PATH--Returns the path of a column value from root to node, with column values separated by char for each row returned by CONNECT BY condition--SYS_CONNECT_BY_PATH(<column>, <char>)--conn scott/tiger

col empname format a20col cbp format a30

SELECT LPAD(' ', 2*LEVEL, ' ' ) || ename empName, dname, job,sys_connect_by_path( ename, '/' ) cbpFROM emp e, dept dWHERE e.deptno = d.deptnoSTART WITH mgr IS NULLCONNECT BY PRIOR empno = mgrORDER SIBLINGS BY job;SELECT LPAD(' ', 2*LEVEL, ' ' ) || ename empName, dname, job,sys_connect_by_path(empno, '.') cbpFROM scott.emp emp, scott.dept deptWHERE emp.deptno = dept.deptnoSTART WITH mgr IS NULLCONNECT BY PRIOR empno = mgrORDER SIBLINGS BY ename; --Function Demo--Use A Function To Receive The Current Node and Search for Parents of the Current NodeCREATE OR REPLACE FUNCTION permissions_sub_tree_root (the_id IN NUMBER,the_level IN NUMBER)RETURN NUMBER ISsub_tree_root NUMBER(10);BEGIN SELECT id INTO sub_tree_root FROM hierarchy WHERE level = the_level -- Connect 'upwards', i.e. find the parent CONNECT BY PRIOR PARENT = id START WITH ID = the_id; RETURN sub_tree_root;

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Introduction to 9i SQL HandbookEND permissions_sub_tree_root;/

SELECT id, name, usernameFROM ( SELECT ID, PARENT, NAME, permissions_sub_tree_root(id, LEVEL) ROOT FROM hierarchy CONNECT BY PRIOR id = PARENT) HIERARCHY, permissionsWHERE ROOT = hierarchy_id; --GROUP BY Demo--Group By Demo with CONNECT_BY_ROOT and CONNECT_BY_PRIOR conn hr/hr SELECT name, SUM(salary) "Total_Salary"FROM ( SELECT CONNECT_BY_ROOT last_name name, salary FROM employees WHERE department_id = 110 CONNECT BY PRIOR employee_id = manager_id)GROUP BY name; --Demos--Indenting conn hr/hr

col lname format a30

SELECT LPAD(' ', level*2, ' ') || last_name LNAME, d.department_idFROM employees e, departments dWHERE e.department_id = d.department_idSTART WITH employee_id = 100CONNECT BY PRIOR e.employee_id = e.manager_id;--Hierarchical Query with IN In a [NOT] IN condition in a WHERE clause, if the right-hand side of the condition is a subquery, you cannot use LEVEL on the left-hand side of the condition. However, you can specify LEVEL in a subquery of the FROM clause to achieve the same result. For example, the following statement is not valid:

SELECT employee_id, last_name FROM employeesWHERE (employee_id, LEVEL)IN (SELECT employee_id, 2 FROM employees)START WITH employee_id = 2CONNECT BY PRIOR employee_id = manager_id;--But the following statement is valid because it encapsulates the query containing the LEVEL information in the FROM clause:

SELECT v.employee_id, v.last_name, v.levFROM ( SELECT employee_id, last_name, LEVEL lev FROM employees v START WITH employee_id = 100 CONNECT BY PRIOR employee_id = manager_id) vWHERE (v.employee_id, v.lev) IN ( SELECT employee_id, 2 FROM employees);

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