Trigger
========================Insert =========================
mysql> create table table1(
-> var1 int(3) NOT NULL,
-> var2 int(3) NOT NULL,
-> sum int(3) NULL
-> );
Query OK, 0 rows affected (0.52 sec)
mysql>
mysql> Create trigger updateSumTable1
-> Before insert
-> On table1
-> For each row
-> Set new.sum=new.var1+new.var2;
Query OK, 0 rows affected (0.08 sec)
mysql>
mysql> insert into table1 values(3,6,null);
Query OK, 1 row affected (0.08 sec)
mysql> select * from table1;
+------+------+------+
| var1 | var2 | sum |
+------+------+------+
| 3 | 6 | 9 |
+------+------+------+
1 row in set (0.10 sec)
========================Delete=========================
mysql> create table table2(
-> var1 int(3) NOT NULL,
-> var2 int(3) NOT NULL,
-> sum int(3) NULL
-> );
Query OK, 0 rows affected (0.52 sec)
mysql> Create trigger updateTable2
-> After delete-> On table1
-> For each row
-> insert into table2 values(old.var1,old.var2,old.sum);
Query OK, 0 rows affected (0.09 sec)
mysql>
mysql> select * from table2;
Empty set (0.00 sec)
mysql>
mysql> delete from table1 where var1=3;
Query OK, 1 row affected (0.11 sec)
mysql> select * from table1;
Empty set (0.00 sec)
mysql> select * from table2;
+------+------+------+
| var1 | var2 | sum |
+------+------+------+
| 3 | 6 | 9 |
+------+------+------+
1 row in set (0.00 sec)
========================UPDATE=========================
mysql> create table table3(
-> var int NOT NULL,
-> sum int NULL
-> );
Query OK, 0 rows affected (0.44 sec)
mysql> DELIMITER //
mysql> Create trigger updateSumTable3
-> Before update
-> On table3
-> For each row
-> begin
-> if(new.var>old.var) then
-> Set new.sum=old.sum+new.var;
-> end if;
-> END //
Query OK, 0 rows affected (0.13 sec)
mysql> DELIMITER ;
mysql> insert into table3 values(3,3);Query OK, 1 row affected (0.12 sec)
mysql> select * from table3;
+-----+------+
| var | sum |
+-----+------+
| 3 | 3 |
+-----+------+
1 row in set (0.00 sec)
mysql> update table3 set var=5 where var=3;
Query OK, 1 row affected (0.18 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from table3;
+-----+------+
| var | sum |
+-----+------+
| 5 | 8 |
+-----+------+
1 row in set (0.00 sec)
mysql> update table3 set var=2 where var=5;
Query OK, 1 row affected (0.36 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from table3;
+-----+------+
| var | sum |
+-----+------+
| 2 | 8 |
+-----+------+
1 row in set (0.00 sec)
');
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