Oracle trigger development

Pay attention to the development of the trigger point

1. Trigger does not receive parameters
2. The more the trigger, the lower the operating performance of DML
3. Trigger a maximum of 32k, if pl / sql statement too much, you can write stored procedures, triggers call
4. In the operative part of the trigger can only DML statements (insert, select, update, delete), you can not use DDL statements (create, alter, drop)
5. Trigger can not contain transaction control statements (commit, rollback, savepoint), as part of a statement trigger is triggered, triggering statement submitted a rollback, the trigger is also committed, rolled back; procedure call trigger body The function can not use transaction control statements
6. Trigger body can not declare any long and blog variables,: new and: old table can not be any long column or blog
7. A table can have a maximum of 12 triggers, and at the same time, the same event, the same type of trigger can only have one, nor contradictions between the various flip-flops

1 --insert事件触发器
2 before insert/before insert for each row
3 after insert/after insert for each row
4 --update事件触发器
5 before update/before update for each row
6 after update/after update for each row
7 --delete事件触发器
8 before delete/before delete for each row
9 after delete/after delete for each row

Trigger enabled and disabled

. 1  - Enable / disable individual flip-flop 
2  ALTER  Trigger trigger_name {enable / disable};
 . 3  - Enable / disable all triggers associated with a particular table 
. 4  ALTER  Table table_name {enable / disable} All Triggers;

Trigger Syntax

. 1  Create  [ or Replace ]  Trigger trigger_name
 2 {before / After} - time to trigger 
. 3 { Delete / INSERT / Update  [ of column ] } - triggering event 
. 4  ON  Table 
. 5  [ for each Row [WHERE (condition) ] ]
 6  DECLARE 
. 7  - local Variables here Wallpaper 
. 8  the begin 
. 9      PL / SQL statement
 10  End ;

Case

1, insert a print data word

1 create or replace trigger trg_test1
2     after insert on table
3 begin
4     dbms_output.put_line('insert successful!')
5 end [trg_test1];

2, the data can not be inserted in the weekend

. 1  Create  or  Replace  Trigger trg_test2
 2      before INSERT  ON  Table 
. 3  DECLARE 
. 4      t_day VARCHAR2 ( 10 );
 . 5  the begin 
. 6      SELECT TO_CHAR (SYSDATE, ' Day ' ) INTO t_day from Dual;
 . 7      IF t_day in ( ' Saturday ' , ' Sunday ' ) the then 
8      - throw an error 
9     RAISE_APPLICATION_ERROR ( - 20001 , ' can not be inserted in the data weekend! ' );
 10      End  IF ;
 . 11  End  [ trg_test2 ] ;

3, use: old and: new

Triggering statement	:old	:new
insert	All fields are null	The data to be inserted
update	Value before the update	The updated value
delete	Value before deleting	All fields are null

 

 

 

. 1  - is determined: updating of the original value must be greater than 
2  Create  or  Replace  Trigger trg_test3
 . 3      before Update  of COL ON  Table 
. 4      for each Row
 . 5  the begin 
. 6      IF : old.col > : new.col the then 
. 7          RAISE_APPLICATION_ERROR ( - 20002 , ' updated values less than the original value can not be updated! ' );
 . 8      End  IF ;
 . 9  End  [ trg_test3 ] ;