information_schema視圖每列返回多個行

Question

我想寫一個查詢，它會給我關於給定的數據庫的列的某些關鍵信息，但到目前爲止我的查詢似乎返回一些奇怪的結果！我需要了解有關色譜柱尺寸，可空性，唯一性等方面的信息。

那麼，爲什麼每列都得到多個結果呢？

SELECT 
C.COLUMN_NAME AS COLUMN_NAME, 
C.TABLE_NAME AS TABLE_NAME, 
C.CHARACTER_MAXIMUM_LENGTH AS CHARACTER_MAXIMUM_LENGTH, 
C.COLUMN_DEFAULT AS COLUMN_DEFAULT, 
C.DATA_TYPE AS DATA_TYPE, 
C.IS_NULLABLE AS IS_NULLABLE, 
CASE WHEN EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE CONSTRAINT_TYPE = 'PRIMARY KEY' 
AND CONSTRAINT_NAME = CC.CONSTRAINT_NAME) THEN 1 ELSE 0 END AS IS_PRIMARY_KEY, 
CASE WHEN EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE CONSTRAINT_TYPE = 'UNIQUE' 
AND CONSTRAINT_NAME = CC.CONSTRAINT_NAME) THEN 1 ELSE 0 END AS IS_UNIQUE, 
C.NUMERIC_PRECISION AS NUMERIC_PRECISION, 
C.NUMERIC_SCALE AS NUMERIC_SCALE, 
FK.TABLE_NAME AS FOREIGN_KEY_TABLE_NAME, 
FK.COLUMN_NAME AS FOREIGN_KEY_COLUMN_NAME 

FROM INFORMATION_SCHEMA.COLUMNS C 
LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CC 
ON C.COLUMN_NAME = CC.COLUMN_NAME 
AND C.TABLE_NAME = CC.TABLE_NAME 
LEFT OUTER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC 
ON CC.CONSTRAINT_NAME = TC.CONSTRAINT_NAME 

LEFT OUTER JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS RC 
ON TC.CONSTRAINT_NAME = RC.CONSTRAINT_NAME 
LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE FC 
ON RC.UNIQUE_CONSTRAINT_NAME = FC.CONSTRAINT_NAME 

LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE FK 
ON FC.COLUMN_NAME = FK.COLUMN_NAME 
AND FC.TABLE_NAME = FK.TABLE_NAME 
WHERE COLUMNPROPERTY(OBJECT_ID(C.TABLE_SCHEMA + '.' + C.TABLE_NAME), C.COLUMN_NAME, 'IsComputed') = 0 
AND TC.CONSTRAINT_TYPE = 'FOREIGN KEY' 

Answer 1

你可能有每列一個以上的約束，因此，如果您使用含有限制信息的意見加入，你會得到多個行，一個用於在列每個約束。

另一個原因可能是相同的列名和表名出現在不同的模式中。

您可以檢查與下面的查詢，這只是表明你出現一次以上的列重複：

WITH a as(
    SELECT 
    C.COLUMN_NAME AS COLUMN_NAME, 
    C.TABLE_NAME AS TABLE_NAME, 
    C.CHARACTER_MAXIMUM_LENGTH AS CHARACTER_MAXIMUM_LENGTH, 
    C.COLUMN_DEFAULT AS COLUMN_DEFAULT, 
    C.DATA_TYPE AS DATA_TYPE, 
    C.IS_NULLABLE AS IS_NULLABLE, 
    CASE WHEN EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE  CONSTRAINT_TYPE = 'PRIMARY KEY' 
    AND CONSTRAINT_NAME = CC.CONSTRAINT_NAME) THEN 1 ELSE 0 END AS IS_PRIMARY_KEY, 
    CASE WHEN EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE  CONSTRAINT_TYPE = 'UNIQUE' 
    AND CONSTRAINT_NAME = CC.CONSTRAINT_NAME) THEN 1 ELSE 0 END AS IS_UNIQUE, 
    C.NUMERIC_PRECISION AS NUMERIC_PRECISION, 
    C.NUMERIC_SCALE AS NUMERIC_SCALE, 
    FK.TABLE_NAME AS FOREIGN_KEY_TABLE_NAME, 
    FK.COLUMN_NAME AS FOREIGN_KEY_COLUMN_NAME 

    FROM INFORMATION_SCHEMA.COLUMNS C 
    LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CC 
    ON C.COLUMN_NAME = CC.COLUMN_NAME 
    AND C.TABLE_NAME = CC.TABLE_NAME 
    LEFT OUTER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC 
    ON CC.CONSTRAINT_NAME = TC.CONSTRAINT_NAME 

    LEFT OUTER JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS RC 
    ON TC.CONSTRAINT_NAME = RC.CONSTRAINT_NAME 
    LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE FC 
    ON RC.UNIQUE_CONSTRAINT_NAME = FC.CONSTRAINT_NAME 

    LEFT OUTER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE FK 
    ON FC.COLUMN_NAME = FK.COLUMN_NAME 
    AND FC.TABLE_NAME = FK.TABLE_NAME 
    WHERE COLUMNPROPERTY(OBJECT_ID(C.TABLE_SCHEMA + '.' + C.TABLE_NAME), C.COLUMN_NAME,  'IsComputed') = 0 
    AND TC.CONSTRAINT_TYPE = 'FOREIGN KEY' 
), b as (
    SELECT COLUMN_NAME, TABLE_NAME 
     FROM a 
    GROUP BY COLUMN_NAME, TABLE_NAME 
    HAVING count(*) > 1 
) 
SELECT a.* 
    FROM a JOIN b ON a.COLUMN_NAME = b.COLUMN_NAME AND a.TABLE_NAME = b.TABLE_NAME 

的CTE a正是從上面查詢。

Answer 2

無論何時將JOIN添加到查詢中，該關係都有可能是一對多的，因此會將結果乘以。你在這裏有5 JOIN，所以大概其中一個陷入了這種情況。

我的猜測是多個約束條件可以應用於單個列，而且您沒有篩選出足夠的可能性來實現這種情況。

關鍵是看看你得到的結果，看看「重複」行中實際上有什麼不同。我有時使用像SELECT C.*, '--' as [--], CC.*, '--' as [--], ...這樣的查詢來顯示所有連接表的所有列。 （as [--]將在Postgres中爲as "--"，在MySQL中爲'--`。）