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ORACLE

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Capabilities of SQL SELECT

StatementsSelectionProjection

Table 1 Table 2

Table 1Table 1

Join

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Selecting All Columns

SELECT *

FROM departments;

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Selecting Specific Columns

SELECT department_id, location_id

FROM departments;

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Alternative Quote (q) Operator

Specify your own quotation mark delimiter.

Choose any delimiter.

Increase readability and usability.

SELECT department_name ||

q'[, it's assigned Manager Id: ]'

|| manager_id

AS "Department and Manager"

FROM departments;

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Using the DESCRIBE Command

DESCRIBE employees

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Using the WHERE Clause

SELECT employee_id, last_name, job_id, department_id

FROM employees

WHERE department_id = 90 ;

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NVL Function

Converts a null value to an actual value: Data types that can be used are date, character, and

number.

Data types must match: NVL(commission_pct,0) NVL(hire_date,'01-JAN-97')

NVL(job_id,'No Job Yet')

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SELECT last_name, salary, NVL(commission_pct, 0),

(salary*12) + (salary*12*NVL(commission_pct, 0)) AN_SAL

FROM employees;

Using the NVL Function

1

2

1 2

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What Are Group Functions?

Group functions operate on sets of rows to

give one result per group.EMPLOYEES

Maximum salary in

EMPLOYEES table

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Obtaining Data from Multiple Tables

EMPLOYEES DEPARTMENTS

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Using a Subquery

to Solve a Problem Who has a salary greater than Abels?

Which employees have salaries greater than

Abels salary?

Main query:

What is Abels salary?

Subquery:

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SELECT last_name, salary

FROM employees

WHERE salary >

(SELECT salary

FROM employeesWHERE last_name = 'Abel');

Using a Subquery

11000

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Creating a Table

by Using a Subquery Create a table and insert rows by combining theCREATE TABLE statement and the AS subqueryoption.

Match the number of specified columns to thenumber of subquery columns.

Define columns with column names and

default values.

CREATE TABLE table

[(column, column...)]AS subquery;

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Implementation of Read Consistency

SELECT *

FROM userA.employees;

UPDATE employees

SET salary = 7000

WHERE last_name = 'Grant';

Data

blocks

Undo

segments

Changedand unchangeddata

Before change

(old data)

User A

User B

Read-

consistentimage

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FLASHBACK TABLE Statement

DROP TABLE emp2;

DROP TABLE succeeded.

FLASHBACK TABLE emp2 TO BEFORE DROP;

FLASHBACK TABLE succeeded.

SELECT original_name, operation, droptimeFROM recyclebin;

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MERGE Statement

Provides the ability to conditionally update or insertdata into a database table

Performs an UPDATE if the row exists, and anINSERT if it is a new row:

Avoids separate updates Increases performance and ease of use

Is useful in data warehousing applications

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MERGE Statement Syntax

You can conditionally insert or update rows in a table by usingthe MERGE statement.

MERGE INTO table_name table_alias

USING (table|view|sub_query) alias

ON

(join condition)WHEN MATCHED THEN

UPDATE SET

col1 = col_val1,

col2 = col2_val

WHENNOT MATCHED THEN

INSERT (column_list)

VALUES (column_values);