如何判斷哪些列已被設置爲mysql中的CASCADE

Question

我很想知道是否有消息告訴哪些列已經使用mysql設置爲CASCADE。做DESC TABLE;似乎沒有產生任何明顯的東西。有什麼建議麼？

Answer 1

由於MySQL的5.1.10，都可以通過加入獲得來自INFORMATION_SCHEMA tables此信息REFERENTIAL_CONSTRAINTS到KEY_COLUMN_USAGE：

SELECT kcu.COLUMN_NAME 
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS rc 
    JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu 
USING (CONSTRAINT_CATALOG, CONSTRAINT_SCHEMA, CONSTRAINT_NAME) 
WHERE 'CASCADE' IN (rc.DELETE_RULE, rc.UPDATE_RULE) 
    AND kcu.TABLE_SCHEMA = DATABASE() 
    AND kcu.TABLE_NAME = 'my_table' 

Answer 2

您可以使用：

show create table tableName; 

這將輸出具有級聯刪除引用一個創建表。

實施例從docs鉤住：

mysql> SHOW CREATE TABLE ibtest11c\G 
*************************** 1. row *************************** 
     Table: ibtest11c 
Create Table: CREATE TABLE `ibtest11c` (
    `A` int(11) NOT NULL auto_increment, 
    `D` int(11) NOT NULL default '0', 
    `B` varchar(200) NOT NULL default '', 
    `C` varchar(175) default NULL, 
    PRIMARY KEY (`A`,`D`,`B`), 
    KEY `B` (`B`,`C`), 
    KEY `C` (`C`), 
    CONSTRAINT `0_38775` FOREIGN KEY (`A`, `D`) 
REFERENCES `ibtest11a` (`A`, `D`) 
ON DELETE CASCADE ON UPDATE CASCADE, // <--- This is what you are looking for 
    CONSTRAINT `0_38776` FOREIGN KEY (`B`, `C`) 
REFERENCES `ibtest11a` (`B`, `C`)  // <--- This is what you are looking for 
ON DELETE CASCADE ON UPDATE CASCADE 
) ENGINE=INNODB CHARSET=latin1 
1 row in set (0.01 sec)