Trigger Blocks : Trigger « Trigger « Oracle PL/SQL Tutorial

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Oracle PL/SQL Tutorial » Trigger » Trigger 
28. 2. 4. Trigger Blocks

Triggers are used to define code that is executed when certain actions or events occur.

The Syntax for Creating a Database Trigger

CREATE [OR REPLACETRIGGER trigger_name
    {BEFORE|AFTERverb_list ON table_name
    [[REFERENCING correlation_namesFOR EACH ROW [WHEN (condition)]]

DECLARE
    declarations
BEGIN
    pl/sql_code
END;

verb_list -- The SQL verbs that fire the trigger.

table_name -- The table on which the trigger is defined.

correlation_names -- Allows you to specify correlation names other than the default of OLD and NEW.

condition -- An optional condition placed on the execution of the trigger.

declarations -- Consists of any variable, record, or cursor declarations needed by this PL/SQL block.

SQL> CREATE TABLE to_table
  2  (col1 NUMBER);

Table created.

SQL>
SQL>
SQL>
SQL> CREATE OR REPLACE TRIGGER before_statement_trigger
  2  BEFORE INSERT ON to_table
  3  BEGIN
  4    DBMS_OUTPUT.PUT_LINE('Before Insert Statement Level');
  5  END;
  6  /

Trigger created.

SQL>
SQL> drop table to_table;

Table dropped.

SQL>
SQL>
SQL> CREATE TABLE to_table
  2  (col1 NUMBER);

Table created.

SQL>
SQL> CREATE OR REPLACE TRIGGER before_row_trigger
  2  BEFORE INSERT ON to_table
  3  FOR EACH ROW
  4  BEGIN
  5    DBMS_OUTPUT.PUT_LINE('Before Insert Row Level');
  6  END;
  7  /

Trigger created.

SQL>
SQL> drop table to_table;

Table dropped.

SQL>
SQL>
28. 2. Trigger
28. 2. 1. Triggers
28. 2. 2. System triggers
28. 2. 3. Creating a Trigger
28. 2. 4. Trigger Blocks
28. 2. 5. Trigger that output old value
28. 2. 6. DML Trigger Example
28. 2. 7. Firing a Trigger
28. 2. 8. The use of a trigger
28. 2. 9. INSERTING, DELETING and UPDATING Predicates
28. 2. 10. Reference current user name in trigger
28. 2. 11. Call raise_application_error to report an error in a trigger
28. 2. 12. Use cursor in trigger
28. 2. 13. Check the status of the trigger
28. 2. 14. Show errors for a trigger
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