This article summarizes some commonly used SQL trigger statements for everyone. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.
1. Create a simple trigger
CREATE TRIGGER 触发器名称 ON 表名 FOR INSERT、UPDATE 或 DELETE AS T-SQL 语句
Note: The trigger name is not quoted.
2. Delete triggers
drop trigger 触发器名称
Delete multiple triggers:
drop trigger 触发器名称,触发器名称
3. Rename triggers
Rename with Query Analyzer
exec sp_rename 原名称, 新名称
sp_rename is a stored procedure that comes with SQL Server. It is used to change the names of user-created objects in the current database, such as table names, lists, index names, etc. .
4. INSERT, UPDATE or DELETE
INSTEAD OF
Execute the trigger statement, but do not execute the SQL statement that triggers the trigger, such as trying to When a record is deleted, the statement specified by the trigger will be executed, and the delete statement will no longer be executed at this time. Example:
create trigger f on tbl instead of delete as insert into Logs...
IF UPDATE(column name)
Check whether a column has been updated. It is used for insert or update, but cannot be used for delete. Example:
create trigger f on tbl for update as if update(status) or update(title) sql_statement --更新了 status 或 title 列
inserted, deleted
These are two virtual tables. inserted saves the table formed by the records affected after insert or update, and deleted saves the table formed before delete or update. The table formed by the affected records. Example:
create trigger tbl_delete on tbl for delete as declare @title varchar(200) select @title=title from deleted insert into Logs(logContent) values('删除了 title 为：' + title + '的记录')
Explanation: If the field value of the field type text or image is retrieved from the inserted or deleted virtual table, the obtained value will be null.
5. View all triggers in the database
use 数据库名 go select * from sysobjects where xtype='TR' sysobjects 保存着数据库的对象，其中 xtype 为 TR 的记录即为触发器对象。在 name 一列，我们可以看到触发器名称。
6. sp_helptext View trigger content
use 数据库名 go exec sp_helptext '触发器名称'
7. sp_helptrigger is used to view the attributes of the trigger.
sp_helptrigger has two parameters: the first parameter is the table name; the second parameter is the trigger type, which is char(6) Type, which can be INSERT, UPDATE, or DELETE. If omitted, the properties of all types of triggers in the specified table will be displayed.
Example:
use 数据库名 go exec sp_helptrigger tbl
8. Recursion, nested triggers
There are two types of recursion, indirect recursion and direct recursion. We explain it with an example as follows. Suppose there are tables 1 and 2 named T1 and T2 respectively, and there are flip-flops G1 and G2 on T1 and T2 respectively.
Indirect recursion: operate on T1 to trigger G1, G1 to operate on T2 to trigger G2, G2 to operate on T1 to trigger G1 again...
Direct recursion: operate on T1 to trigger G1 , G1 operates on T1 to trigger G1 again...
Nested trigger
is similar to indirect recursion. Indirect recursion must form a loop, while nested triggers do not necessarily have to form a loop. A ring can be triggered continuously from T1->T2->T3... in this way, allowing up to 32 levels of nesting.
Set direct recursion
By default, direct recursion is prohibited. There are two methods to set it to allow:
T-SQL: exec sp_dboption 'dbName', ' recursive triggers', true
EM: Right click on the database->Properties->Options.
Set indirect recursion and nesting
By default, indirect recursion and nesting are allowed. There are two ways to disable it:
T-SQL: exec sp_configure 'nested triggers', 0 --The second parameter is 1, which means it is allowed
EM: Right click on the registration->Properties->Server Settings.
9. Trigger rollback
We have seen that many registration systems cannot change the user name after registration, but this is mostly determined by the application. If By directly opening the database table to make changes, you can also change its user name. By using rollback in the trigger, you can cleverly realize that the user name cannot be changed.
use 数据库名 go create trigger tr on 表名 for update as if update(userName) rollback tran
The key lies in the last two sentences, which are explained as follows: If the userName column is updated, roll back the transaction.
10. Disable and enable triggers
Disable: alter table table name disable trigger trigger name
Enable: alter table table name enable trigger Trigger name
If there are multiple triggers, separate the trigger names with commas.
If you replace "Trigger Name" with "ALL", it means disabling or enabling all triggers of the table.
11. Determine insertion, modification and deletion
create TRIGGER [updatetest] ON [dbo].[TEST] FOR INSERT, UPDATE, DELETE AS begin DECLARE @IsInsert bit, @IsUpdate bit, @IsDelete bit IF EXISTS(SELECT 1 FROM inserted) AND NOT EXISTS(SELECT 1 FROM deleted) SET @IsInsert = 1 ELSE SET @IsInsert = 0 IF EXISTS(SELECT 1 FROM inserted) AND EXISTS(SELECT 1 FROM deleted) SET @IsUpdate = 1 ELSE SET @IsUpdate = 0 IF NOT EXISTS(SELECT 1 FROM inserted) AND EXISTS(SELECT 1 FROM deleted) SET @IsDelete = 1 ELSE SET @IsDelete = 0 if (@IsUpdate=1) PRINT 'updated ' if (@IsInsert=1) PRINT 'insert ' if (@IsDelete=1) PRINT 'delete 'end
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