Deletingl i Rows Based on Another Tablele

Use subqueries in DELETE statements to remove rows from a table based on values from another table.

6 rows deleted.

9-22

Deletingl i Rows:

IntegrityI i Constrainti Error

9-23

Database Transactionsi

Consist of one of the following statements:

•• DML statementst t ts thatt t make up one consistenti t t change toto thet datata

•• One DDL statementt t t

•• One DCL statementt t t

9-24

Database Transactionsi

•• Beginin when thet firstfir t executablet le SQL statementt t t isis executedt

•• End withith one off thet followingf ll i events:t :

–COMMITIT orr ROLLBACK

–DDL orr DCL statementt t t executest (automatic( t tic commit)it)

–Userr exitsits

–Systemt crashesr

9-25

Advantages of COMMITIT

and ROLLBACK

•• Ensurere datata consistencyi t

•• Previewr i datata changes beforef re makingi changes permanentr t

•• Groupr logicallyl i lly relatedr l t operationsr ti

9-26

Controllinglli Transactionsi

Transactioni

ROLLBACK to Savepoint B

9-27

ImplicitI li it Transactioni Processingi

•• An automatict tic commitit occursrs underr thet followingf ll i circumstances:ir t :

–A DDL statementt t t isis issuedi

–A DCL statementt t t isis issuedi

–A normalr l exitit fromfr SQL*Plus,* l , withoutit t explicitlyli itly issuingi i COMMITIT orr ROLLBACK

•• An automatict tic rollbackr ll occursrs underr an abnormalr l terminationt r i ti off SQL*Plus* l orr a systemt failuref il re

9-28

State of the Data Before COMMITIT or ROLLBACK

•• The previousr i statet te off thet datata can be recoveredr r ..

•• The currentrr t userr can reviewr i thet resultsr lts off thet

DML operationsr ti by usingi thet SELECT statementt t t..

•• Othert r usersrs cannott viewi thet resultsr lts off thet

DML statementst t ts by thet currentrr t userr..

•• The affectedff t rowsr arere lockedl ;; othert r usersrs cannott change thet datata withinit in thet affectedff t rowsr ..

9-29

State of the Data After COMMITIT

•• Datata changes arere made permanentr t inin thet databaset ..

•• The previousr i statet te off thet datata isis permanentlyr tly lostl t..

•• Allll usersrs can viewi thet resultsr lts..

•• Locks on thet affectedff t rowsr arere released;r l ; thoset rowsr arere availableil le forf r othert r usersrs toto manipulatei l te..

•• Allll savepointsi ts arere erasedr ..

9-30

Committingi i Data

1 row updated.

•• Commitit thet changes..

SQL> COMMIT;

Commit complete.

9-31