如何检查列是否已经是外键？

Question

我有一个名为Person的表和名为ID的列如何检查ID是否已经是FOREIGN KEY因为我想使用这段代码:

ALTER TABLE Person ADD FOREIGN KEY(ID) REFERENCES Job(ID)
ON DELETE CASCADE ON UPDATE CASCADE

但如果ID已经是FOREIGN KEY,它会给我以下错误"可能导致循环或多个级联路径",因为有两个级联的条件...如何检查此字段是否为FOREIGN KEY以避免此错误？

Answer 1

你想查看INFORMATION SCHEMA视图

虽然它没有那么完整.这是您想要的最终查询:

SELECT 
     KCU1.CONSTRAINT_NAME AS 'FK_CONSTRAINT_NAME'
   , KCU1.TABLE_NAME AS 'FK_TABLE_NAME'
   , KCU1.COLUMN_NAME AS 'FK_COLUMN_NAME'
   , KCU1.ORDINAL_POSITION AS 'FK_ORDINAL_POSITION'
   , KCU2.CONSTRAINT_NAME AS 'UQ_CONSTRAINT_NAME'
   , KCU2.TABLE_NAME AS 'UQ_TABLE_NAME'
   , KCU2.COLUMN_NAME AS 'UQ_COLUMN_NAME'
   , KCU2.ORDINAL_POSITION AS 'UQ_ORDINAL_POSITION'
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS RC
JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE KCU1
ON KCU1.CONSTRAINT_CATALOG = RC.CONSTRAINT_CATALOG 
   AND KCU1.CONSTRAINT_SCHEMA = RC.CONSTRAINT_SCHEMA
   AND KCU1.CONSTRAINT_NAME = RC.CONSTRAINT_NAME
JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE KCU2
ON KCU2.CONSTRAINT_CATALOG = 
RC.UNIQUE_CONSTRAINT_CATALOG 
   AND KCU2.CONSTRAINT_SCHEMA = 
RC.UNIQUE_CONSTRAINT_SCHEMA
   AND KCU2.CONSTRAINT_NAME = 
RC.UNIQUE_CONSTRAINT_NAME
   AND KCU2.ORDINAL_POSITION = KCU1.ORDINAL_POSITION

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http://msdn.microsoft.com/en-us/library/aa175805(v=sql.80).aspx