[英]Unique constraint that check two columns in MySQL
I would like to add a unicity constraint on my MySQL table.我想在我的 MySQL 表上添加一个唯一性约束。 This table contains four columns :该表包含四列:
ID | NAME | ADDRESS1 | ADDRESS2
This constraint must check that for a new row, the new address1
and address2
are not contained either in ADDRESS1
nor ADDRESS2
.此约束必须检查新行的新address1
和address2
不包含在ADDRESS1
和ADDRESS2
。
Example :例子 :
INSERT INTO MYTABLE (ADDRESS1, ADDRESS2) values ('A', 'B'); -- OK
INSERT INTO MYTABLE (ADDRESS1, ADDRESS2) values ('C', 'D'); -- OK
INSERT INTO MYTABLE (ADDRESS1, ADDRESS2) values ('E', 'A'); -- Fails because A exists in ADDRESS1
INSERT INTO MYTABLE (ADDRESS1, ADDRESS2) values ('D', 'F'); -- Fails because D exists in ADDRESS2
Is there a way to define a such constraint ?有没有办法定义这样的约束?
You can do it with a BEFORE
trigger this way您可以通过这种方式使用BEFORE
触发器来完成
CREATE TRIGGER tg_bi_mytable
BEFORE INSERT ON mytable
FOR EACH ROW
SET NEW.address1 = IF(EXISTS
(
SELECT *
FROM mytable
WHERE address1 IN(NEW.address1, NEW.address2)
OR address2 IN(NEW.address1, NEW.address2)
), NULL, NEW.address1);
Note: Since you're using a MySQL version that lacks SIGNAL
the trick is to violate NOT NULL
constraint on one of the columns when rows with the same address have been found.注意:由于您使用的是缺少SIGNAL
的 MySQL 版本,因此当找到具有相同地址的行时,将违反其中一列的NOT NULL
约束。
Here is SQLFiddle demo.这是SQLFiddle演示。 Uncomment one of the last insert statements and click Build Schema
.取消对最后一个插入语句之一的注释,然后单击Build Schema
。 These inserts won't succeed.这些插入不会成功。
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