SQL DDL QUERIESCS 260

Database Systems

Introduction to DDL

Data Definition Language (DDL) Used to create and modify database objects

In contrast to DML (data manipulation language) used to view, insert, update, and delete data in those database objects

These database objects include tables, views, users, sequences, and stored programs

Common DDL commands CREATE ALTER DROP

DDL commands modify the database as soon as they are issued

Overview

Creating tables CREATE Naming practices Data types

Specifying constraints Modifying/dropping tables

Creating Tables

To create a table, use the CREATE command

Syntax

The <data_type> may also identify the field’s storage capacity

CREATE TABLE <table_name> (<field1_name> <data_type>,<field2_name> <data_type>,…<fieldN_name> <data_type>

);

Creating Tables

Oracle example

CREATE TABLE student( student_id NUMBER(6), student_name VARCHAR2(30), student_DOB DATE);

Overview

Creating tables CREATE Naming practices Data types

Specifying constraints Modifying/dropping tables

Naming Practices

Naming tables and fields Oracle database table and field names

must conform to the Oracle naming standard 1 to 30 characters long Must begin with a character Can contain characters, numbers, $, _ and #

Each table must have a name that is unique in its schema

Each field must have a name that is unique in its table

Naming Practices

Good table naming practices Name every table using a combination of

two words Separate words in tables names using an

underscore Use the same descriptive first word for all

related table names Makes it easier to see related tables

Naming Practices

Good field naming practices Name every field using a combination of

two words, with the first word indicating the table name Makes it easier to identify the table that a field

belongs to when writing/analyzing a query involving multiple tables

Don’t do this for foreign keys Use the name that is in the parent table instead

Overview

Creating tables CREATE Naming practices Data types

Characters Numbers Dates Objects

Specifying constraints Modifying/dropping tables

Data Types

When creating tables, each field’s data type must be specified Specifies the type of data stored in the field May include the field’s storage capacity

Purposes Dictates the internal encoding Optimizes internal storage use Provides error checking

Data Types

Characters Oracle

CHAR, NCHAR VARCHAR2,

NVARCHAR2 CLOB

MySQL CHAR VARCHAR TEXT

Data Types

CHAR, NCHAR (Oracle) and CHAR (MySQL) Fixed-length character strings Trailing blank spaces are padded to meet the

specified capacity Useful for fields where fixed width values are

expected Oracle

Maximum of 2,000 characters

Must specify capacity NCHAR uses Unicode

encoding while CHAR uses the server platform’s default encoding scheme

MySQL Maximum of 255

characters Capacity specification

unnecessary (default is 1)

CHAR, NCHAR (Oracle) and CHAR (MySQL) Examples

Oracle

MySQL

Data Types

CREATE TABLE <table_name> ( student_gender CHAR(1));

CREATE TABLE <table_name> ( student_gender CHAR);

Data Types

VARCHAR2, NVARCHAR2 (Oracle) and VARCHAR (MySQL) Variable-length character strings No trailing space padding to meet the specified capacity Useful for fields where fixed width values are not

expected

Oracle Maximum of 4,000

characters Must specify capacity NVARCHAR2 uses Unicode

encoding while VARCHAR2 uses the server platform’s default encoding scheme

MySQL Maximum of 255

characters Must specify capacity

VARCHAR2, NVARCHAR2 (Oracle) and VARCHAR (MySQL) Examples

Oracle

MySQL

Data Types

CREATE TABLE <table_name> ( student_name VARCHAR2(30));

CREATE TABLE <table_name> ( student_name VARCHAR(30));

Data Types

CLOB (Oracle) and TEXT (MySQL) Stores large amounts of variable-length character

strings Useful for fields where large amounts of variable

width values are expected

Oracle Up to 4GB of data No capacity

specification Also has LONG (2GB)

for legacy purposes

MySQL Up to 64K of data No capacity

specification Also has TINYTEXT

(255 bytes), MEDIUMTEXT (16MB), and LONGTEXT (4GB)

CLOB (Oracle) and TEXT (MySQL) Examples

Oracle

MySQL

Data Types

CREATE TABLE <table_name> ( student_summary CLOB);

CREATE TABLE <table_name> ( student_summary MEDIUMTEXT);

Data Types

Numbers Use for data that is entirely numeric

Not always the case for phone numbers, postal codes, social security numbers, etc.

Oracle NUMBER

MySQL INT DOUBLE DECIMAL (NUMERIC)

Data Types

Numbers in Oracle NUMBER

Precision and scale may be specified Precision: total number of digits Scale: number of digits to the right of the

decimal point If neither is specified, the maximum values are

used Allows values from 10-130 and 10126

If only one value is specified, then the value applies to the precision

Data Types

Numbers in Oracle NUMBER

Examples

CREATE TABLE <table_name> ( student_age NUMBER(2));

CREATE TABLE <table_name> ( item_price NUMBER(5,2));

Data Types

Numbers in MySQL INT

Signed or unsigned integers Can specify number of digits (up to 11) Also has TINYINT, SMALLINT, MEDIUMINT and BIGINT

DOUBLE Signed floating point numbers Can specify the precision and scale (defaults to 16 and 4) Also has FLOAT (less precise)

DECIMAL (NUMERIC) Signed floating point numbers Must specify the precision and scale Can be more precise than DOUBLE or FLOAT but takes more

space

Data Types

Numbers in MySQL Number examples

CREATE TABLE <table_name> ( student_age INT(2));

CREATE TABLE <table_name> ( item_price DECIMAL(5,2));

Data Types

Dates in Oracle DATE

Stores dates between 1/1/4712 BC and 12/31/9999

Consists of both a date and a time component Default date format: ‘DD-MON-YY’ If a date is specified without a time component,

the default time is midnight 24-hour clock time: 00:00:00

Format: ‘HH24:MI:SS’ 12-hour clock time: 12:00:00

Format: ‘HH12:MI:SS’

Data Types

Dates in MySQL DATE

Stores dates between 1/1/1000 and 12/31/9999 Consists of a date component only Default date format: ‘YYYY-MM-DD’

DATETIME Consists of both date and timestamp

components Date example (both Oracle and MySQL)

CREATE TABLE <table_name> ( student_dob DATE);

Data Types

Objects Oracle

BLOB BFILE

MySQL BLOB

BLOB is an acronym for “binary large object”

Data Types

Objects in Oracle BLOB

Stores large amounts of variable-length binary data (images, files, etc.)

Can optionally specify a capacity (default is 2GB) Maximum capacity is 8TB Significant overhead (treated by DBMS much like

other data) BFILE

Stores a reference (directory and file name) to a binary file on the database server

Maximum file size is 4GB

Data Types

Objects in MySQL BLOB

Like in Oracle, stores large amounts of variable-length binary data (images, files, etc.)

Cannot specify a capacity Maximum capacity of 64K Also has TINYBLOB (255 bytes), MEDIUMBLOB

(16MB), and LONGBLOB (4GB) Significant overhead (as in Oracle)

Data Types

Object examples Both Oracle and MySQL

Oracle BFILE example

Use the “BFILENAME” function when inserting values to a BFILE field

CREATE TABLE student ( student_image BLOB);

CREATE TABLE student2 ( student_image BFILE);

INSERT INTO student2 VALUES( BFILENAME(‘directory’, ‘filename.ext’));

Overview

Creating tables Specifying constraints

Primary keys Foreign keys Composite keys NOT NULL DEFAULT UNIQUE CHECK conditions

Modifying/dropping tables

Constraints

Constraints are rules that restrict the values that can be entered into a column or table

Table level constraints Specified after the comma separated list of

fields in the create table statement Column level constraints

Specified with the associated column in the comma separated list of fields in the create table statement

Some column constraints can be specified at the table level, but not vice versa

Constraints

Constraint naming conventions Some constraints, like primary keys and foreign

keys, are named Convention: tablename_fieldname_constraintType

constraintTypes Primary keys: pk Foreign keys: fk

Limited to 30 characters Oracle assigns system generated names if none

are provided User provided constraint names are far more readable

MySQL primary keys are always named “PRIMARY”

Constraints

Viewing constraints Oracle

Oracle provided constraint names will begin with “SYS_”

MySQL

SELECT constraint_nameFROM user_constraintsWHERE table_name = ‘<table name>’

SELECT index_nameFROM information_schema.table_constraintsWHERE constraint_schema = ‘<schema>’;

Primary Keys

Primary key creation syntax

CREATE TABLE <table_name> ( <pk_field_name> <type> PRIMARY KEY, … <fieldN_name> <type>);

CREATE TABLE <table_name>( <pk_field_name> <type>, … <fieldN_name> <type>, CONSTRAINT <constraint_name> PRIMARY KEY (<pk_field_name>));

Single column primary keys can be specified at the column level

Alternatively, primary keys can be specified at the table-level

Foreign Keys

Foreign key rules A foreign key MUST have the same data type as the

parent primary key field A foreign key SHOULD have the same size as the

parent primary key field A foreign key SHOULD have the same field name as

the parent primary key field A foreign key MUST be designated as such after the

parent primary key field has been designated as a pk Knowing this, in what order must the tables in our candy

database be created (assuming pks/fks are created at the same time as their corresponding tables)?

Sample Database (CANDY)CUST_ID CUST_NAME CUST_TYPE CUST_ADDR CUST_ZIP CUST_PHONE USERNAME PASSWORD

1 Jones, Joe P 1234 Main St. 91212 434-1231 jonesj 12342 Armstrong,Inc. R 231 Globe Blvd. 91212 434-7664 armstrong 33333 Sw edish Burgers R 1889 20th N.E. 91213 434-9090 sw edburg 23534 Pickled Pickles R 194 CityView 91289 324-8909 pickpick 53335 The Candy Kid W 2121 Main St. 91212 563-4545 kidcandy 23516 Waterman, Al P 23 Yankee Blvd. 91234 w ateral 89007 Bobby Bon Bons R 12 Nichi Cres. 91212 434-9045 bobbybon 30118 Crow sh, Elias P 7 77th Ave. 91211 434-0007 crow el 10339 Montag, Susie P 981 Montview 91213 456-2091 montags 9633

10 Columberg Sw eets W 239 East Falls 91209 874-9092 columsw e 8399

PURCH_ID PROD_ID CUST_ID PURCH_DATE DELIVERY_DATE POUNDS STATUS

1 1 5 28-Oct-04 28-Oct-04 3.5 PAID2 2 6 28-Oct-04 30-Oct-04 15 PAID3 1 9 28-Oct-04 28-Oct-04 2 PAID3 3 9 28-Oct-04 28-Oct-04 3.7 PAID4 3 2 28-Oct-04 3.7 PAID5 1 7 29-Oct-04 29-Oct-04 3.7 NOT PAID5 2 7 29-Oct-04 29-Oct-04 1.2 NOT PAID5 3 7 29-Oct-04 29-Oct-04 4.4 NOT PAID6 2 7 29-Oct-04 3 PAID7 2 10 29-Oct-04 14 NOT PAID7 5 10 29-Oct-04 4.8 NOT PAID8 1 4 29-Oct-04 29-Oct-04 1 PAID8 5 4 29-Oct-04 7.6 PAID9 5 4 29-Oct-04 29-Oct-04 3.5 NOT PAID

PROD_ID PROD_DESC PROD_COSTPROD_PRICE

1 Celestial Cashew Crunch 7.45$ 10.00$

2 Unbrittle Peanut Paradise 5.75$ 9.00$

3 Mystery Melange 7.75$ 10.50$

4 Millionaire’s Macadamia Mix 12.50$ 16.00$

5 Nuts Not Nachos 6.25$ 9.50$

CUST_TYPE_IDCUST_TYPE_DESC

P Private

R Retail

W Wholesale

CANDY_CUSTOMER

CANDY_PURCHASE

CANDY_CUST_TYPE

CANDY_PRODUCT

Foreign Keys

Foreign key creation syntaxCREATE TABLE candy_customer ( <fk_field_name> <type> REFERENCES <parent_table>(<parent_table_pk_field_name>), … <fieldN_name> <type>);

CREATE TABLE candy_customer ( <fk_field_name> <type>, … <fieldN_name> <type>, CONSTRAINT <constraint_name> FOREIGN KEY (<fk_field_name>) REFERENCES <parent_table>(<parent_table_pk_field_name>));

Foreign keys in Oracle can be specified at the column level

Alternatively, foreign keys can be specified at the table-level

Composite Keys

A composite key can be created only after you define the fields that make up the composite key (at the table-level)

Convention: constraint_name should consist of a combination of all fields names in the composite key (limited to 30 characters)

CREATE TABLE <table_name>( <ck_field1_name> <type>, <ck_field2_name> <type>, … <fieldN_name> <type>, CONSTRAINT <constraint_name> PRIMARY KEY (<ck_field1_name>, <ck_field2_name>));

NOT NULL

Requires a column’s values to be non-null

CREATE TABLE <table_name>( <fieldM_name> <type> NOT NULL, … <fieldN_name> <type>);

CREATE TABLE <table_name>( <fieldM_name> <type> CONSTRAINT <constraint_name> NOT NULL, … <fieldN_name> <type>);

Works in both Oracle and MySQL

Works in Oracle only

DEFAULT

Provides a default column value if no value is provided when data is inserted Default values may be hardcoded or use

functions Syntax

Example

CREATE TABLE <table_name>( <fieldM_name> <type> DEFAULT <value>);

CREATE TABLE student( date_added DATE DEFAULT SYSDATE);

UNIQUE

Requires all column values to be unique A table can have only one primary key but

can have many unique columns Syntax and example

CREATE TABLE <table_name>( <fieldM_name> <type>, … <fieldN_name> <type>, CONSTRAINT <constraint_name> UNIQUE (<fieldM_name>));

CREATE TABLE student( student_id NUMBER(9) PRIMARY KEY, … student_username VARCHAR2(20), CONSTRAINT student_username_uk UNIQUE (student_username));

CHECK Conditions

Restricts a column’s value to one or more possible values (not supported in MySQL) Still allows NULL and/or empty strings

Syntax and example

CREATE TABLE student ( student_gender VARCHAR(1), CONSTRAINT student_gender_ck CHECK (student_gender IN (‘M’,’F’)));

CREATE TABLE <table_name>( <field1_name> <type>, … <fieldN_name> <type>, CONSTRAINT <constraint_name> CHECK (<condition>));

Overview

Creating tables Specifying constraints Modifying/dropping tables

Modifying Database Tables

Allowed modifications Changing a table or column name Adding a new column Deleting a primary key or foreign key constraint

Allowed if existing data fits new specifications Changing a column’s data type, size, or default

value Adding a primary key or foreign key constraint Adding a CHECK condition constraint Adding a NOT NULL or UNIQUE constraint

Modifying Database Tables

Add column

Modify column syntax

Remove column syntax

ALTER TABLE <table_name> ADD <field_name> <datatype> <constraints>

ALTER TABLE <table_name> MODIFY <field_name> <datatype> <constraints>

ALTER TABLE <table_name> DROP COLUMN <field_name>

ALTER TABLE student ADD student_age NUMBER(2) NOT NULL

ALTER TABLE student MODIFY student_age NUMBER(3) NOT NULL

ALTER TABLE student DROP COLUMN student_age

Modifying Database Tables

Add constraint syntax

Remove constraint syntax Oracle

MySQL

ALTER TABLE <table_name> ADD CONSTRAINT constraint_name <constraint> (<column(s)>)

ALTER TABLE <table_name> DROP CONSTRAINT <constraint_name>

ALTER TABLE student ADD CONSTRAINT student_pk PRIMARY KEY (student_id)

ALTER TABLE student DROP CONSTRAINT student_pk

ALTER TABLE student DROP PRIMARY KEY

ALTER TABLE <table_name> DROP PRIMARY KEY

Modifying Database Tables

Delete table syntax

A table cannot be dropped if its primary key is referenced as a foreign key in other tables

In Oracle, you can remove constraints simultaneously

In MySQL, you first need to remove the foreign key constraints for each foreign key

DROP TABLE <table_name>

DROP TABLE <table_name> CASCADE CONSTRAINTS

ALTER TABLE <table_name_with_fk> DROP FOREIGN KEY <foreign_key_name>

DROP TABLE <table_name_with_pk>

Modifying Database Tables

Debugging DDL Commands Attempt to identify trivial errors by

comparing the command with the error message/position

Take an incremental approach Create the table one field at a time until you

find the field that is causing the problem Modify one column at a time

Multiple modifications could be performed in a single statementALTER TABLE student MODIFY student_age NUMBER(3) NOT NULLADD CONSTRAINT student_pk PRIMARY KEY (student_id)