C# 如何检查列是否已经是外键？

我有一个名为Person的表和一个名为ID的列 如何检查ID是否已经是外键，因为我想使用以下代码：

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

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但如果ID已经是外键，它会给我以下错误“可能导致循环或多个级联路径”，因为存在两个级联的情况。。。如何检查此字段是否为外键以避免此错误？

您需要查看

信息架构

视图

虽然它并不像应该的那么完整。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

有关更多信息，请参见此处

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这是一个简单的小版本

SELECT TOP(1) a.COLUMN_NAME FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS b JOIN 
                INFORMATION_SCHEMA.KEY_COLUMN_USAGE a ON a.CONSTRAINT_CATALOG = b.CONSTRAINT_CATALOG AND a.CONSTRAINT_NAME = b.CONSTRAINT_NAME WHERE a.COLUMN_NAME = *your column*)

您还可以在where子句中轻松添加表名和数据库名