day2 session2

8/12/2019 day2 session2

1/30

Entry Level Technology Program

Satyam Learning Center ORACLE 1 of 1

Database Transactions

Begin when the first DML SQL statement isexecuted

End with one of the following events:A COMMIT or ROLLBACK statement is issued

A DDL or DCL statement executes (automaticcommit)

The user exits iSQL*PlusThe system crashes


2/30



Advantages of COMMITand ROLLBACKStatements

With COMMITand ROLLBACKstatements, you can:

Ensure data consistency

Preview data changes before making changespermanent

Group logically related operations


3/30



Controlling Transactions

SAVEPOINT B

SAVEPOINT A

DELETE

INSERT

UPDATE

INSERT

COMMITTime

Transaction

ROLLBACK

to SAVEPOINT B

ROLLBACK

to SAVEPOINT AROLLBACK


4/30



UPDATE...

SAVEPOINT update_done;Savepoint created.

INSERT...ROLLBACK TO update_done;

Rollback complete.

Rolling Back Changesto a Marker

Create a marker in a current transaction by usingthe SAVEPOINT statement.

Roll back to that marker by using the ROLLBACK

TO SAVEPOINT statement.


5/30



State of the Data afterCOMMIT

Data changes are made permanent in thedatabase.

The previous state of the data is permanently lost.

All users can view the results.

Locks on the affected rows are released; thoserows are available for other users to manipulate.

All savepoints are erased.


6/30



COMMIT;

Commit complete.

Make the changes.

Commit the changes.

DELETE FROM EMP

WHERE EMPNO = 7639;

1 row deleted.

INSERT INTO DEPT

VALUES (290, 'Corporate Tax', NULL, 1700);

1 row inserted.

Committing Data


7/30



State of the Data After ROLLBACK

Discard all pending changes by using theROLLBACK

statement:

Data changes are undone.

Previous state of the data is restored.

Locks on the affected rows are released.

DELETE FROM copy_emp;

22 rows deleted.

ROLLBACK;

Rollback complete.


8/30



Summary

Description

Adds a new row to the table

Modifies existing rows in the table

Removes existing rows from the table

Makes all pending changes permanent

Is used to rollback to the savepoint marker

Discards all pending data changes

Statement

INSERT

UPDATE

DELETE

COMMIT

SAVEPOINT

ROLLBACK

In this lesson, you should have learned how to useDML statements and control transactions.


9/30



Producing Readable Outputwith iSQL*Plus


10/30



Substitution Variables

I want to query

different values.... salary = ?

department_id = ?

... last_name = ? ...

User


11/30



Substitution Variables

Use iSQL*Plus substitution variables to:

Temporarily store values

Single ampersand (&)

Double ampersand (&&)

DEFINEcommand

Pass variable values between SQL statements

Dynamically alter headers and footers


12/30



Specifying Column Names,Expressions, and Text

Use substitution variables to supplement thefollowing:

WHEREconditions ORDER BYclauses

Column expressions

Table names

Entire SELECTstatements


13/30



SELECT employee_id, last_name, job_id,

&column_name

FROM employees

WHERE &condition

ORDER BY &order_column ;

Specifying Column Names,Expressions, and Text


14/30



Exercise

Query I from exe-I document


15/30



Displaying Datafrom Multiple Tables


16/30


17/30



Equijoin

Non-equijoin

Outer join

Self join

Types of Joins

Oracle Proprietary

Joins (8iand prior):


18/30



Joining Tables Using Oracle Syntax

Use a join to query data from more than one table.

Write the join condition in the WHERE clause.

Prefix the column name with the table name when thesame column name appears in more than one table.

Efficiency of joins increases when we join from thetable where less number of rows are there to thetable where more number of rows.

SELECT table1.column, table2.columnFROM table1, table2

WHERE table1.column1 =table2.column2;


19/30



What is an Equijoin?

EMPLOYEES DEPARTMENTS

Foreign key Primary key


20/30



Using the UNION ALL

Operator

Display the current and previous departments of all employees.

SELECT EMPNO, JOB, DEPTNO

FROM EMP

UNION ALL

SELECT EMPNO, JOB, DEPTNO

FROM JOB_HISTORY

ORDER BY EMPNO;


21/30



The INTERSECTOperator

A B


22/30



Using the INTERSECT

Operator

Display the employee IDs and job IDs of employeeswho currently have a job title that they held beforebeginning their tenure with the company.

SELECT EMPNO, JOB

FROM EMP

INTERSECT

SELECT EMPNO, JOB

FROM JOB_HISTORY;


23/30



TheMINUSOperator

A B


24/30



TheMINUSOperator

Display the employee IDs of those employees who havenot changed their jobs even once.

SELECT EMPNO,JOB

FROM EMP

MINUS

SELECT EMPNO,JOB

FROM JOB_HISTORY;


25/30



SETOperator Guidelines

The expressions in the SELECT lists must match innumber and data type.

Parentheses can be used to alter the sequence of

execution. The ORDER BY clause:

Can appear only at the very end of thestatement

Will accept the column name, aliases from thefirst SELECT statement, or the positionalnotation


26/30



The Oracle Server and SET

Operators

Duplicate rows are automatically eliminatedexcept in UNION ALL.

Column names from the first query appear in theresult.

The output is sorted in ascending order by defaultexcept in UNION ALL.


27/30


28/30



Matching the SELECTStatement

Using the UNION operator, display the employee ID, job ID,and salary of all employees.

SELECT EMPNO, JOB,SAL

FROM EMP

UNION

SELECT EMPNO, JOB,0

FROM JOB_HISTORY;


29/30



Summary

In this lesson, you should have learned how to:

Use UNIONto return all distinct rows

Use UNION ALLto returns all rows, including duplicates Use INTERSECTto return all rows shared by

both queries

Use MINUSto return all distinct rows selected by the firstquery but not by the second

Use ORDER BYonly at the very end ofthe statement


30/30


Exercise

Query III from exe-I document

day2 session2

Documents

Transcript of day2 session2