探討SQL利用INFORMATION_SCHEMA系統視圖如何獲取表的主外鍵信息

2020-01-18 23:37:38

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接著上篇文章《解析SQL 表結構信息查詢含主外鍵、自增長》里面提到了INFORMATION_SCHEMA視圖，其實到了SQL 2005微軟都主推大家使用INFORMATION_SCHEMA系統視圖，而不是在使用sys東東了，當然目前還是有許多信息只能通過sys視圖來查詢。這里我們還是以查詢表結果信息為例來說明一些主要的INFORMATION_SCHEMA視圖的使用。
首先我們需要查詢列的信息，這需要用到[INFORMATION_SCHEMA].[COLUMNS]系統視圖來查詢數據列的信息，SQL 如下：

復制代碼代碼如下:

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'

運行結果如下：

我們都知道我們在定義列的時候一般的使用都是varchar(50)之類的信息，這里我們需要整合DATA_TYPE和CHARACTER_MAXIMUM_LENGTH信息，當CHARACTER_MAXIMUM_LENGTH為-1時即使說沒有指定具體最大長度，數據的指定長度信息是max，而numeric需要整合NUMERIC_PRECISION、NUMERIC_SCALE信息。修改后的SQL如下：

復制代碼代碼如下:

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

運行結果如圖：

現在我們需要標記這張表的那些列是主鍵，那些列是外鍵，要查詢表的主、外鍵信息需要用到[INFORMATION_SCHEMA].[TABLE_CONSTRAINTS]和[INFORMATION_SCHEMA].[KEY_COLUMN_USAGE] 系統視圖
運行結果如圖：

修改我們先前的SQL語句：

復制代碼代碼如下:

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

運行結果如圖：

現在我們已經知道那些列是主鍵那些是外鍵，接下來的就是外鍵列所關聯的外檢表信息，這里需要用到[INFORMATION_SCHEMA].[REFERENTIAL_CONSTRAINTS]系統視圖，運行該視圖如下：

所以修改我們的SQL如下：

復制代碼代碼如下:

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

運行結果如圖：

我們的查詢結果中顯示了太多的NULL，看著不怎么舒服，還有我們的表名應該顯示一次就可以，修改SQL如下：

復制代碼代碼如下:

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