查找表的所有外键的最有效方法是啥？

Posted 2023-02-24

【中文标题】查找表的所有外键的最有效方法是啥？

【英文标题】：What is the most efficient way to find all foreign keys for a table?查找表的所有外键的最有效方法是什么？

【发布时间】：2021-02-10 06:59:19

【问题描述】：

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如下查询：

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`

查看示例答案：

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?

但在一个中等大小的数据库中（总大小约为 20GB，大约 20 个数据库之间有 1000-10000 个表），这可能需要几秒钟（在我的系统上每次查询几乎需要 3 秒）。

有没有更有效的方法来获取它们？

注意：我使用的是 mysql 5.7。

【参考方案1】：

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

我首先尝试反转连接顺序，但没有帮助，或者将 where 放在 key_column_usage 表上，但没有帮助。不过，显式引用连接两侧的架构和表就可以了。

在任何情况下，以下查询平均耗时 1-2 毫秒，而上述查询平均耗时不到 3 秒（数字取自 performance_schema 中的 1000 个左右的查询）。

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`

【参考方案2】：

这将为您提供有关外键的所有信息

还有更多信息，leke referencd column 和 refrencd table

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

另外在 mysql 5.7 中有这个选项，但仅适用于 innodb 表

 SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN

给你一个类型

TYPE 一组位标志，其中包含有关外键列的信息，OR 运算在一起。 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

【讨论】：

这很有趣。我会试着找点时间看看加入那张桌子是否更快。我想根据我下面的回答将连接分成两个查询（或运行你的两个查询）可能也会很快，因为看起来你只需要从字面上引用表/模式而不是通过连接来使其快速.