探讨SQL利用INFORMATION_SCHEMA系统视图如何获取表的主外键信息

2022-11-12 09:27:49

内容摘要

这篇文章主要为大家详细介绍了探讨SQL利用INFORMATION_SCHEMA系统视图如何获取表的主外键信息，具有一定的参考价值，可以用来参考一下。对此感兴趣的朋友，看看idc笔记做的技术

文章正文

这篇文章主要为大家详细介绍了探讨SQL利用INFORMATION_SCHEMA系统视图如何获取表的主外键信息，具有一定的参考价值，可以用来参考一下。

对此感兴趣的朋友，看看idc笔记做的技术笔记！

接着上篇文章《解析SQL 表结构信息查询含主外键、自增长》里面提到了INFORMATION_SCHEMA视图，其实到了SQL 2005微软都主推大家使用INFORMATION_SCHEMA系统视图，而不是在使用sys东东了，当然目前还是有许多信息只能通过sys视图来查询。这里我们还是以查询表结果信息为例来说明一些主要的INFORMATION_SCHEMA视图的使用。首先我们需要查询列的信息，这需要用到[INFORMATION_SCHEMA].[COLUMNS]系统视图来查询数据列的信息，SQL 如下：

代码如下:


SELECT c.TABLE_SCHEMA ,
 c.TABLE_NAME ,
 c.COLUMN_NAME ,
 c.DATA_TYPE ,
 c.CHARACTER_MAXIMUM_LENGTH ,
 c.COLUMN_DEFAULT ,
 c.IS_NULLABLE ,
 c.NUMERIC_PRECISION ,
 c.NUMERIC_SCALE
FROM [INFORMATION_SCHEMA].[COLUMNS] c
WHERE TABLE_NAME = 'Address'

运行结果如下：我们都知道我们在定义列的时候一般的使用都是varchar(50)之类的信息，这里我们需要整合DATA_TYPE和CHARACTER_MAXIMUM_LENGTH信息，当CHARACTER_MAXIMUM_LENGTH为-1时即使说没有指定具体最大长度，数据的指定长度信息是max，而numeric需要整合NUMERIC_PRECISION、NUMERIC_SCALE信息。修改后的SQL如下：

代码如下:


SELECT c.TABLE_SCHEMA ,
 c.TABLE_NAME ,
 c.COLUMN_NAME ,
 CASE WHEN ( ( CHARINDEX('char', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH <> -1
 )
 THEN c.DATA_TYPE + '('
 + CAST(c.CHARACTER_MAXIMUM_LENGTH AS VARCHAR(4)) + ')'
 WHEN ( ( CHARINDEX('CHAR', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH = -1
 ) THEN c.DATA_TYPE + '(max)'
 WHEN ( CHARINDEX('numeric', c.DATA_TYPE) > 0 )
 THEN c.DATA_TYPE + '(' + CAST(c.NUMERIC_PRECISION AS VARCHAR(4))
 + ',' + CAST(c.NUMERIC_SCALE AS VARCHAR(4)) + ')'
 ELSE c.DATA_TYPE
 END AS DATA_TYPE ,
 c.COLUMN_DEFAULT ,
 c.IS_NULLABLE ,
 c.COLUMN_DEFAULT
FROM [INFORMATION_SCHEMA].[COLUMNS] c
WHERE TABLE_NAME = 'Address'
ORDER BY c.ORDINAL_POSITION

运行结果如图：现在我们需要标记这张表的那些列是主键，那些列是外键，要查询表的主、外键信息需要用到[INFORMATION_SCHEMA].[TABLE_CONSTRAINTS]和[INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] 系统视图运行结果如图：修改我们先前的SQL语句：

代码如下:


SELECT c.TABLE_SCHEMA ,
 c.TABLE_NAME ,
 c.COLUMN_NAME ,
 CASE WHEN ( ( CHARINDEX('char', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH <> -1
 )
 THEN c.DATA_TYPE + '('
 + CAST(c.CHARACTER_MAXIMUM_LENGTH AS VARCHAR(4)) + ')'
 WHEN ( ( CHARINDEX('CHAR', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH = -1
 ) THEN c.DATA_TYPE + '(max)'
 WHEN ( CHARINDEX('numeric', c.DATA_TYPE) > 0 )
 THEN c.DATA_TYPE + '(' + CAST(c.NUMERIC_PRECISION AS VARCHAR(4))
 + ',' + CAST(c.NUMERIC_SCALE AS VARCHAR(4)) + ')'
 ELSE c.DATA_TYPE
 END AS DATA_TYPE ,
 c.COLUMN_DEFAULT ,
 c.IS_NULLABLE ,
 c.COLUMN_DEFAULT ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'PRIMARY KEY' THEN 'YES'
 ELSE 'NO'
 END AS IS_PRIMARY_KEY ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'FOREIGN KEY' THEN 'YES'
 ELSE 'NO'
 END AS IS_FOREIGN_KEY
FROM [INFORMATION_SCHEMA].[COLUMNS] c
 LEFT JOIN [INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] kcu ON kcu.TABLE_SCHEMA = c.TABLE_SCHEMA
 AND kcu.TABLE_NAME = c.TABLE_NAME
 AND kcu.COLUMN_NAME = c.COLUMN_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[TABLE_CONSTRAINTS] tc ON tc.CONSTRAINT_SCHEMA = kcu.CONSTRAINT_SCHEMA
 AND tc.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME
WHERE c.TABLE_NAME = 'Address'
ORDER BY c.ORDINAL_POSITION

运行结果如图：现在我们已经知道那些列是主键那些是外键，接下来的就是外键列所关联的外检表信息，这里需要用到[INFORMATION_SCHEMA].[REFERENTIAL_CONSTRAINTS]系统视图，运行该视图如下：所以修改我们的SQL如下：

代码如下:


SELECT c.TABLE_SCHEMA ,
 c.TABLE_NAME ,
 c.COLUMN_NAME ,
 CASE WHEN ( ( CHARINDEX('char', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH <> -1
 )
 THEN c.DATA_TYPE + '('
 + CAST(c.CHARACTER_MAXIMUM_LENGTH AS VARCHAR(4)) + ')'
 WHEN ( ( CHARINDEX('CHAR', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH = -1
 ) THEN c.DATA_TYPE + '(max)'
 WHEN ( CHARINDEX('numeric', c.DATA_TYPE) > 0 )
 THEN c.DATA_TYPE + '(' + CAST(c.NUMERIC_PRECISION AS VARCHAR(4))
 + ',' + CAST(c.NUMERIC_SCALE AS VARCHAR(4)) + ')'
 ELSE c.DATA_TYPE
 END AS DATA_TYPE ,
 c.COLUMN_DEFAULT ,
 c.IS_NULLABLE ,
 c.COLUMN_DEFAULT ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'PRIMARY KEY' THEN 'YES'
 ELSE 'NO'
 END AS IS_PRIMARY_KEY ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'FOREIGN KEY' THEN 'YES'
 ELSE 'NO'
 END AS IS_FOREIGN_KEY,
 fkcu.COLUMN_NAME AS FOREIGN_KEY,
 fkcu.TABLE_NAME AS FOREIGN_TABLE
FROM [INFORMATION_SCHEMA].[COLUMNS] c
 LEFT JOIN [INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] kcu ON kcu.TABLE_SCHEMA = c.TABLE_SCHEMA
 AND kcu.TABLE_NAME = c.TABLE_NAME
 AND kcu.COLUMN_NAME = c.COLUMN_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[TABLE_CONSTRAINTS] tc ON tc.CONSTRAINT_SCHEMA = kcu.CONSTRAINT_SCHEMA
 AND tc.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[REFERENTIAL_CONSTRAINTS] fc ON kcu.CONSTRAINT_SCHEMA = fc.CONSTRAINT_SCHEMA
 AND kcu.CONSTRAINT_NAME = fc.CONSTRAINT_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] fkcu ON fkcu.CONSTRAINT_SCHEMA = fc.UNIQUE_CONSTRAINT_SCHEMA
 AND fkcu.CONSTRAINT_NAME = fc.UNIQUE_CONSTRAINT_NAME
WHERE c.TABLE_NAME = 'Address'
ORDER BY c.ORDINAL_POSITION

运行结果如图：我们的查询结果中显示了太多的NULL，看着不怎么舒服，还有我们的表名应该显示一次就可以，修改SQL如下：

代码如下:


SELECT CASE WHEN c.ORDINAL_POSITION = 1
 THEN c.TABLE_SCHEMA + '.' + c.TABLE_NAME
 ELSE ''
 END AS TABLE_NAME ,
 c.COLUMN_NAME ,
 CASE WHEN ( ( CHARINDEX('char', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH <> -1
 )
 THEN c.DATA_TYPE + '('
 + CAST(c.CHARACTER_MAXIMUM_LENGTH AS VARCHAR(4)) + ')'
 WHEN ( ( CHARINDEX('CHAR', c.DATA_TYPE) > 0
 OR CHARINDEX('binary', c.DATA_TYPE) > 0
 )
 AND c.CHARACTER_MAXIMUM_LENGTH = -1
 ) THEN c.DATA_TYPE + '(max)'
 WHEN ( CHARINDEX('numeric', c.DATA_TYPE) > 0 )
 THEN c.DATA_TYPE + '(' + CAST(c.NUMERIC_PRECISION AS VARCHAR(4))
 + ',' + CAST(c.NUMERIC_SCALE AS VARCHAR(4)) + ')'
 ELSE c.DATA_TYPE
 END AS DATA_TYPE ,
 ISNULL(c.COLUMN_DEFAULT, '') AS COLUMN_DEFAULT ,
 CASE WHEN c.IS_NULLABLE = 'YES' THEN '√'
 ELSE ''
 END IS_NULLABLE ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'PRIMARY KEY' THEN '√'
 ELSE ''
 END AS IS_PRIMARY_KEY ,
 CASE WHEN tc.CONSTRAINT_TYPE = 'FOREIGN KEY' THEN '√'
 ELSE ''
 END AS IS_FOREIGN_KEY ,
 ISNULL(fkcu.COLUMN_NAME, '') AS FOREIGN_KEY ,
 ISNULL(fkcu.TABLE_NAME, '') AS FOREIGN_TABLE
FROM [INFORMATION_SCHEMA].[COLUMNS] c
 LEFT JOIN [INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] kcu ON kcu.TABLE_SCHEMA = c.TABLE_SCHEMA
 AND kcu.TABLE_NAME = c.TABLE_NAME
 AND kcu.COLUMN_NAME = c.COLUMN_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[TABLE_CONSTRAINTS] tc ON tc.CONSTRAINT_SCHEMA = kcu.CONSTRAINT_SCHEMA
 AND tc.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[REFERENTIAL_CONSTRAINTS] fc ON kcu.CONSTRAINT_SCHEMA = fc.CONSTRAINT_SCHEMA
 AND kcu.CONSTRAINT_NAME = fc.CONSTRAINT_NAME
 LEFT JOIN [INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] fkcu ON fkcu.CONSTRAINT_SCHEMA = fc.UNIQUE_CONSTRAINT_SCHEMA
 AND fkcu.CONSTRAINT_NAME = fc.UNIQUE_CONSTRAINT_NAME
WHERE c.TABLE_NAME = 'Address'
ORDER BY c.ORDINAL_POSITION

运行结果如图：有不对的地方还请大家拍砖！

注：关于探讨SQL利用INFORMATION_SCHEMA系统视图如何获取表的主外键信息的内容就先介绍到这里，更多相关文章的可以留意

代码注释

上一篇基于MySQL数据库复制Master-Slave架构的分析下一篇 MySQL 精简过程(删除一些文件)

作者：喵哥笔记

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