循环永远不会在SQL Server中使用While Exists结束

Question

While Exists (Select * From Col Where Depth Is Null)
    Update T
    Set T.Depth = P.Depth + 1,
        T.Lineage = P.Lineage + LTrim(Str(T.ParentId, 6, 0)) + '/'
    From Col T
    Join Col P On T.ParentId = P.Id
    Where
        P.Depth >= 0
        And P.Lineage Is Not Null
        And T.Depth Is Null

Answer 1

看起来你正在尝试进行递归查询，标准的方法是使用CTE：

;WITH rec AS(
SELECT c.Id, c.Depth, CAST(c.Id AS varchar(MAX) + '/' AS Lineage
    FROM Col c
    WHERE c.ParentId IS NULL
    UNION ALL
    SELECT c1.Id, rec.Depth + 1, rec.Lineage + CAST(c1.id as varchar(10)) + '/'
    FROM rec
    INNER JOIN Col c1 on rec.Id = c1.ParentId
    WHERE rec.Depth < 100 --Limit the recursion, set this to what is appropriate for your data
)
--SELECT * FROM rec --Use this first to see if the data is correct, then:
UPDATE T
SET T.Depth = r.Depth, T.Lineage = r.Lineage
FROM Col T
INNER JOIN rec r ON T.Id = r.Id

有关CTE的更多信息，您可以查看this technet link。