触发器学习

数据库表：

创建语句：

--table1

CREATE TABLE [dbo].[table1](     [id] [int] IDENTITY(1,1) NOT NULL,     [value] [varchar](10) NULL, CONSTRAINT [PK_table] PRIMARY KEY CLUSTERED (     [id] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY]

--table2

CREATE TABLE [dbo].[table2](     [id] [int] IDENTITY(1,1) NOT NULL,     [count] [int] NOT NULL, CONSTRAINT [PK_table2] PRIMARY KEY CLUSTERED (     [id] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY]

insert into table2(count) values(0)

--触发器语句，对table1进行插入或者删除操作会触发触发器更新table1的行数

CREATE TRIGGER insert_table1 ON table1

    FOR INSERT , DELETE

    AS BEGIN

        UPDATE table2 set count=(SELECT count(*) FROM table1) WHERE id=1;

    END; ===============================================================================================================================================

触发器知识：

一般格式：

CREATE TRIGGER <触发器名>

    {BEFORE | AFTER} <触发事件> ON <表名>

    FOR EACH {ROW | STATEMENT}

    [WHEN <触发条件>]

    <触发动作体>

触发事件：可以是INSERT、DELETE或UODATE，也可以是几个事件的组合。

触发器类型：可以分为行级触发器（FOR EACH ROW）和语句级触发器（FOR EACH STATEMENT）