Jag tror att det berodde på en förväxling med FOR EACH ROW
uttalande.
Det är endast för "matchade poster för uttalandet som utfärdades innan utlösaren anropas. "
Om det finns N
antal poster i en tabell och matchar poster för where id=x
,
förutsatt x
orsakar ett resultat som är mindre än N
poster, säg N-5
, sedanFOR EACH ROW
orsakar en loop för N-5
endast gånger.
UPPDATERA :
En provkörning på de rader som påverkas på grund av FOR EACH ROW
uttalande visas nedan.
mysql> -- create a test table
mysql> drop table if exists tbl; create table tbl ( i int, v varchar(10) );
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.06 sec)
mysql> -- set test data
mysql> insert into tbl values(1,'one'),(2,'two' ),(3,'three'),(10,'ten'),(11,'eleven');
Query OK, 5 rows affected (0.02 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from tbl;
+------+--------+
| i | v |
+------+--------+
| 1 | one |
| 2 | two |
| 3 | three |
| 10 | ten |
| 11 | eleven |
+------+--------+
5 rows in set (0.02 sec)
mysql> select count(*) row_count from tbl;
+-----------+
| row_count |
+-----------+
| 5 |
+-----------+
1 row in set (0.00 sec)
mysql>
mysql> -- record loop count of trigger in a table
mysql> drop table if exists rows_affected; create table rows_affected( i int );
Query OK, 0 rows affected (0.02 sec)
Query OK, 0 rows affected (0.05 sec)
mysql> select count(*) 'rows_affected' from rows_affected;
+---------------+
| rows_affected |
+---------------+
| 0 |
+---------------+
1 row in set (0.00 sec)
mysql>
mysql> set @cnt=0;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> -- drop trigger if exists trig_bef_del_on_tbl;
mysql> delimiter //
mysql> create trigger trig_bef_del_on_tbl before delete on tbl
-> for each row begin
-> set @cnt = if(@cnt is null, 1, (@cnt+1));
->
-> /* for cross checking save loop count */
-> insert into rows_affected values ( @cnt );
-> end;
-> //
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> delimiter ;
mysql>
mysql> -- now let us test the delete operation
mysql> delete from tbl where i like '%1%';
Query OK, 3 rows affected (0.02 sec)
mysql>
mysql> -- now let us see what the loop count was
mysql> select @cnt as 'cnt';
+------+
| cnt |
+------+
| 3 |
+------+
1 row in set (0.00 sec)
mysql>
mysql> -- now let us see the table data
mysql> select * from tbl;
+------+-------+
| i | v |
+------+-------+
| 2 | two |
| 3 | three |
+------+-------+
2 rows in set (0.00 sec)
mysql> select count(*) row_count from tbl;
+-----------+
| row_count |
+-----------+
| 2 |
+-----------+
1 row in set (0.00 sec)
mysql> select count(*) 'rows_affected' from rows_affected;
+---------------+
| rows_affected |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql>