FOR EACH ROW表示每個匹配行的更新或刪除.

除非查詢中有where條件,否則觸發器主體不會遍歷整個表數據.

下面演示了一個工作示例：

創建樣本表：

drop table if exists tbl_so_q23374151;

create table tbl_so_q23374151 ( i int, v varchar(10) );

-- set test data

insert into tbl_so_q23374151

values (1,'one'),(2,'two' ),(3,'three'),(10,'ten'),(11,'eleven');

-- see current data in table**:

select * from tbl_so_q23374151;

+------+--------+

| i | v |

+------+--------+

| 1 | one |

| 2 | two |

| 3 | three |

| 10 | ten |

| 11 | eleven |

+------+--------+

5 rows in set (0.00 sec)

用于記錄觸發器主體中循環計數的樣本表：

-- let us record, loop count of trigger, in a table

drop table if exists tbl_so_q23374151_rows_affected;

create table tbl_so_q23374151_rows_affected( i int );

select count(*) as rows_affected from tbl_so_q23374151_rows_affected;

+---------------+

| rows_affected |

+---------------+

| 0 |

+---------------+

定義刪除觸發器：

drop trigger if exists trig_bef_del_on_tbl_so_q23374151;

delimiter //

create trigger trig_bef_del_on_tbl_so_q23374151 before delete on tbl_so_q23374151

for each row begin

set @cnt = if(@cnt is null, 1, (@cnt+1));

/* for cross checking save loop count */

insert into tbl_so_q23374151_rows_affected values ( @cnt );

end;

//

delimiter ;

現在,測試刪除操作：

delete from tbl_so_q23374151 where i like '%1%';

-- now let us see what the loop count was

select @cnt as 'cnt';

+------+

| cnt |

+------+

| 3 |

+------+

現在,檢查主表上的觸發效果：

-- now let us see the table data

select * from tbl_so_q23374151;

+------+-------+

| i | v |

+------+-------+

| 2 | two |

| 3 | three |

+------+-------+

2 rows in set (0.00 sec)

select count(*) as rows_affected from tbl_so_q23374151_rows_affected;

+---------------+

| rows_affected |

+---------------+

| 3 |

+---------------+

1 row in set (0.00 sec)

總結

以上是生活随笔為你收集整理的mysql 触发器 for each row 理解_“for each row”如何在mysql中的触发器中工作？的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。