如何查询外键 onupdate/ondelete？答案

【问题标题】：How to query for foreign key onupdate/ondelete?如何查询外键 onupdate/ondelete？
【发布时间】：2016-07-26 16:26:27
【问题描述】：

我有以下查询来返回外键详细信息：

SELECT
    tc.constraint_name,
    tc.table_name,
    kcu.column_name,
    ccu.table_schema AS foreign_table_schema,
    ccu.table_name AS foreign_table_name,
    ccu.column_name AS foreign_column_name,
    pg_catalog.pg_get_constraintdef(pg_constraint.oid, true) AS foreign_definition
FROM
    information_schema.table_constraints AS tc
    JOIN information_schema.key_column_usage AS kcu
      ON tc.constraint_name = kcu.constraint_name
    JOIN information_schema.constraint_column_usage AS ccu
      ON ccu.constraint_name = tc.constraint_name
    JOIN pg_constraint
      ON pg_constraint.conname = tc.constraint_name
WHERE constraint_type = 'FOREIGN KEY'

由此，我可以获得重建外键所需的大部分信息。唯一缺少的是关于更新和删除信息（尽管这可以从foreign_definition 中解析出来）。我一直在想办法在不解析的情况下接收这些详细信息，但到目前为止我还没有运气。

有没有人知道我可以找到哪个表的更新和删除详细信息？

这是专门为 Postgres 设计的。

【问题讨论】：

你试过information_schema.referential_constraints吗？..有两列update_rule和delete_rule

标签： sql database postgresql database-schema

【解决方案1】：

像这样？..

SELECT
    tc.constraint_name,
    tc.table_name,
    kcu.column_name,
    ccu.table_schema AS foreign_table_schema,
    ccu.table_name AS foreign_table_name,
    ccu.column_name AS foreign_column_name,
    pg_catalog.pg_get_constraintdef(pg_constraint.oid, true) AS foreign_definition,
    update_rule,
    delete_rule
FROM
    information_schema.table_constraints AS tc
    JOIN information_schema.key_column_usage AS kcu
      ON tc.constraint_name = kcu.constraint_name
    JOIN information_schema.constraint_column_usage AS ccu
      ON ccu.constraint_name = tc.constraint_name
    JOIN pg_constraint
      ON pg_constraint.conname = tc.constraint_name
    LEFT OUTER JOIN information_schema.referential_constraints rc on tc.constraint_name = rc.constraint_name and ccu.table_schema = rc.constraint_schema

WHERE constraint_type = 'FOREIGN KEY'

【讨论】：