Question

我在PhpMyAdmin中使用MySQL。我正在寻找一种方法来对表格施加约束，以便：

column1(int) + column2(int) + column3(int) <= 100

Answer 1

到目前为止，在mysql中你不能在表定义中有这样的约束。您可以使用应用程序层来验证这一点。如果你想使用mysql，那么你可以使用signal使用触发器并引发错误 https://dev.mysql.com/doc/refman/5.5/en/signal.html

触发器的外观如下

delimiter //
create trigger check_col_sum before insert on test
for each row
begin
 if (new.column1+new.column2+new.column3) > 100 then 
  signal sqlstate '45000' set message_text = 'Sum of column1,column2 and column3 must be less than equal to 100';
 end if;
end;//

delimiter ;

测试用例

mysql> create table test (id int auto_increment primary key, column1 int, column2 int, column3 int);
Query OK, 0 rows affected (0.14 sec)

mysql> delimiter //
mysql> create trigger check_col_sum before insert on test
    -> for each row
    -> begin
    ->  if (new.column1+new.column2+new.column3) > 100 then 
    ->   signal sqlstate '45000' set message_text = 'Sum of column1,column2 and column3 must be less than equal to 100';
    ->  end if;
    -> end;//
Query OK, 0 rows affected (0.09 sec)

mysql> 
mysql> delimiter ;


mysql> insert into test (column1,column2,column3) values (10,20,30);
Query OK, 1 row affected (0.08 sec)

mysql> select * from test ;
+----+---------+---------+---------+
| id | column1 | column2 | column3 |
+----+---------+---------+---------+
|  1 |      10 |      20 |      30 |
+----+---------+---------+---------+
1 row in set (0.00 sec)



mysql> insert into test (column1,column2,column3) values (10,20,80);
ERROR 1644 (45000): Sum of column1,column2 and column3 must be less than equal to 100
mysql> select * from test ;
+----+---------+---------+---------+
| id | column1 | column2 | column3 |
+----+---------+---------+---------+
|  1 |      10 |      20 |      30 |
+----+---------+---------+---------+
1 row in set (0.00 sec)

Answer 2

您可以使用MySQL5.7的新功能生成列，您可以在创建表时在第三列中定义两列的总和，或者可以通过 ALTER <添加列/ strong>命令。实施例

CREATE TABLE triangle( sidea DOUBLE, sideb DOUBLE, sidec DOUBLE AS (SQRT(sidea * sidea + sideb * sideb)) );

参考链接：

Clone

列值的总和约束MySQL

2 个答案: