TSQL函数和Check约束以确保表中存在父值

Posted 2021-02-26

If a "InReplyToID" is provided, it must be a valid MessageId

ALTER TABLE [dbo].[Message]  WITH CHECK ADD  CONSTRAINT [CK_Message] CHECK  (([InReplyToId] IS NULL OR [dbo].[CheckInReplyToMessageId]([InReplyToId])>=(0)))
GO
ALTER TABLE [dbo].[Message] CHECK CONSTRAINT [CK_Message]
 
 
 
CREATE FUNCTION [dbo].[CheckInReplyToMessageId] 
(
    @MessageId BIGINT
)
RETURNS bit
AS
BEGIN
    DECLARE @RetVal bit
 
    SET @RetVal = (SELECT MessageId
                     FROM Message
                     WHERE MessageId = @MessageId)
 
    RETURN isnull(@RetVal, 0)
 
END