Oracle triggers are database objects that execute business rules or actions when a specific event, such as insertion, update, or delete, occur. To create a trigger, you need to follow the following steps: 1. Create a trigger, specify the name, event, table, and FOR EACH ROW; 2. Write the trigger code, perform verification, recording, calling stored procedures, etc.; 3. Specify the trigger timing (BEFORE, AFTER, or INSTEAD OF); 4. Compile the trigger.
How to write Oracle triggers
Oracle triggers are database objects that are automatically executed when a specified event occurs. Triggers are used to apply business rules or perform specific actions when performing SQL operations, such as inserting, updating, or deleting.
General steps to write an Oracle trigger:
1. Create a trigger:
<code class="sql">CREATE TRIGGER <trigger_name> BEFORE | AFTER | INSTEAD OF <event> ON <table_name> FOR EACH ROW AS BEGIN -- 觸發(fā)器代碼END;</table_name></event></trigger_name></code>
-
trigger_name: The name of the trigger. -
event: The event that the trigger will target, such asINSERT,UPDATE, orDELETE. -
table_name: The table to which the trigger will be applied. -
FOR EACH ROW: Specifies that the trigger will be executed on each line affected.
2. Write trigger code:
The trigger code can perform various operations, such as:
- Verify or modify data for insert/update/delete operations.
- Record operation details (for example, operation user, operation time).
- Calling stored procedures or functions to perform more complex logic.
3. Specify the triggering time:
Triggers can be specified to execute at three times:
-
BEFORE: Execute before performing an operation. -
AFTER: Execute after the operation is executed. -
INSTEAD OF: Replace the execution of the operation.
4. Compile trigger:
After creating the trigger, you need to compile it by running the following command:
<code class="sql">ALTER TRIGGER <trigger_name> COMPILE;</trigger_name></code>
Example: Verify data before INSERT operation
<code class="sql">CREATE TRIGGER validate_insert_data BEFORE INSERT ON employees FOR EACH ROW BEGIN IF :NEW.salary </code>
This trigger will be executed before performing the INSERT operation and checks whether the value of salary field in the newly inserted row is greater than 10,000. If not, an application error will be raised.
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