校验插入指定结点是否导致编码循环的示例函数

CREATE FUNCTION f_CheckCode(
@ID char(3), --要插入的节点编码
@PID char(3) --要插入的节点的上级编码
)RETURNS bit
AS
BEGIN
   DECLARE @t TABLE(ID char(3),Level int,Flag tinyint)
   DECLARE @level int
   SET @level=0
   INSERT @t SELECT ID,@level,CASE WHEN ID=@PID THEN 1 ELSE 0 END
   FROM tb
   WHERE PID=@ID
   WHILE @@ROWCOUNT>0
       AND NOT EXISTS(SELECT * FROM @t WHERE Flag=1)
   BEGIN
       SET @level=@level+1
       INSERT @t SELECT ID,@level,CASE WHEN ID=@PID THEN 1 ELSE 0 END
       FROM tb a,@t b
       WHERE a.PID=b.ID
           AND b.Level=@level-1
   END
   RETURN((SELECT MAX(Flag) FROM @t))
END

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