Bagaimana cara kerja setiap baris di pemicu di mysql?

FOR EACH ROW berarti untuk setiap baris yang cocok yang mendapatkan diperbarui atau dihapus .

Isi pemicu tidak akan mengulang seluruh data tabel kecuali ada kondisi where dalam kueri.

Contoh kerja ditunjukkan di bawah ini:

Buat tabel contoh :

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)

Tabel contoh untuk merekam jumlah putaran di badan pemicu :

-- 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 |
+---------------+

Tentukan hapus pemicu :

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 ;

Sekarang, uji hapus operasi :

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

-- now let us see what the loop count was
select @cnt as 'cnt';
+------+
| cnt  |
+------+
|    3 |
+------+

Sekarang, periksa efek pemicu pada tabel utama :

-- 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)