查找表的所有外键的最有效方法是什么？

如何解决查找表的所有外键的最有效方法是什么？

如何最有效地获取外键信息（包括更新/删除规则）？

最明显的方法是使用类似以下查询的内容：

SELECT 
`RC` . `CONSTRAINT_CATALOG` AS `fkCatalog`,`RC` . `CONSTRAINT_SCHEMA` AS `fkSchema`,`RC` . `CONSTRAINT_NAME` AS `fkName`,`RC` . `UPDATE_RULE` AS `onUpdate`,`RC` . `DELETE_RULE` AS `onDelete`,`RC` . `TABLE_NAME` AS `fkTable`,`RC` . `REFERENCED_TABLE_NAME` AS `refTable`,`KCU` . `COLUMN_NAME` AS `fkColumn`,`KCU` . `REFERENCED_COLUMN_NAME` AS `refColumn`,`KCU` . `ORDINAL_POSITION` AS `fkOrdinal` 
FROM 
`informatION_SCHEMA` . `referential_CONSTRAINTS` AS `RC` 
INNER JOIN `informatION_SCHEMA` . `KEY_COLUMN_USAGE` AS `KCU` 
ON 
`KCU` . `CONSTRAINT_SCHEMA` = `RC` . `CONSTRAINT_SCHEMA` AND 
`KCU` . `CONSTRAINT_NAME` = `RC` . `CONSTRAINT_NAME` 
WHERE 
`RC` . `CONSTRAINT_SCHEMA` = ? AND 
`RC` . `TABLE_NAME` = ? 
ORDER BY 
`RC` . `REFERENCED_TABLE_NAME`,`KCU` . `ORDINAL_POSITION`

例如查看答案：

How to find all tables that have foreign keys that reference particular table.column and have values for those foreign keys?

https://dba.stackexchange.com/questions/102371/how-to-check-foreign-keys-related-to-a-table

How to find all tables that have foreign keys that reference particular table.column and have values for those foreign keys?

但是在中等大小的数据库（总大小约为20GB，在约20个数据库之间有1000-10000个表）中，这可能要花费几秒钟的时间（在我的系统上，每个查询将近3秒）。

是否有更有效的方式来获取它们？

注意：我正在使用MysqL 5.7。

解决方法

一种解决方案最终是在联接的两侧显式引用表和架构。我知道information_schema表（尤其是在MySQL

我首先尝试颠倒连接顺序，这无济于事，或者将where放在key_column_usage表上，这无济于事。显式引用联接两侧的模式和表确实可以解决问题。

无论如何，以下查询平均花费1-2毫秒，而上面的查询平均花费不到3秒（从Performance_schema的1000多个查询中提取的数字）。

SELECT 
`RC` . `CONSTRAINT_CATALOG` AS `fkCatalog`,`RC` . `CONSTRAINT_SCHEMA` AS `fkSchema`,`RC` . `CONSTRAINT_NAME` AS `fkName`,`RC` . `UPDATE_RULE` AS `onUpdate`,`RC` . `DELETE_RULE` AS `onDelete`,`RC` . `TABLE_NAME` AS `fkTable`,`RC` . `REFERENCED_TABLE_NAME` AS `refTable`,`KCU` . `COLUMN_NAME` AS `fkColumn`,`KCU` . `REFERENCED_COLUMN_NAME` AS `refColumn`,`KCU` . `ORDINAL_POSITION` AS `fkOrdinal` 
FROM 
`INFORMATION_SCHEMA` . `KEY_COLUMN_USAGE` AS `KCU` 
INNER JOIN 
`INFORMATION_SCHEMA` . `REFERENTIAL_CONSTRAINTS` AS `RC` 
ON 
`KCU` . `CONSTRAINT_SCHEMA` = `RC` . `CONSTRAINT_SCHEMA` AND 
`KCU` . `CONSTRAINT_NAME` = `RC` . `CONSTRAINT_NAME` 
WHERE 
`KCU` . `TABLE_SCHEMA` = ? AND -- The addition of this and the next row are the only real difference.
`KCU` . `TABLE_NAME` = ? AND 
`RC` . `CONSTRAINT_SCHEMA` = ? AND 
`RC` . `TABLE_NAME` = ? 
ORDER BY 
`KCU` . `REFERENCED_TABLE_NAME`,`KCU` . `ORDINAL_POSITION`

,

这将为您提供有关外键的所有信息

还有更多信息，例如参考列和刷新表

SELECT 
   TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME
   FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
   WHERE REFERENCED_TABLE_SCHEMA IS NOT NULL;

此外，在mysql 5.7中有此选项，但仅适用于innodb表

 SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN

哪个给你类型

TYPE包含有关外键列信息的位标志的集合，或在一起。 1 = ON DELETE CASCADE，2 = ON UPDATE SET NULL，4 = ON UPDATE CASCADE，8 = ON UPDATE SET NULL，16 = ON DELETE NO ACTION，32 = ON UPDATE NO ACTION。

http://mysql.babo.ist/#/en/innodb-sys-foreign-table.html