具有 2 个并集的公用表表达式计数器答案

【问题标题】：Common Table Expression Counters with 2 Unions具有 2 个并集的公用表表达式计数器
【发布时间】：2011-02-18 13:47:36
【问题描述】：

如果我有一个有母亲和父亲的家庭的公用表表达式，我如何增加“世代”计数器？一个家庭应该将孩子作为第 0 代，将父母作为第 1 代，将四个祖父母作为第 2 代。但是循环执行两次，每组祖父母执行一次。

;WITH FamilyTree
AS
(
    SELECT *, 0 AS Generation
    FROM myTable
    WHERE [id] = 99

    UNION ALL
    SELECT name, Generation + 1
    FROM myTable AS Fam
    INNER JOIN FamilyTree
    ON Fam.[id] = FamilyTree.[motherid]

    UNION ALL
    SELECT name, Generation + 1
    FROM myTable AS Fam
    INNER JOIN FamilyTree
    ON Fam.[id] = FamilyTree.[fatherid]
)
SELECT generation, name FROM FamilyTree

【问题讨论】：

标签： sql sql-server tsql recursion common-table-expression

【解决方案1】：

一口气改变一个代沟里的亲戚看看，而不是在CTE中有2个递归子句。这两个子句形成一个部分交叉连接，这就是为什么你有额外的行

;WITH FamilyTree
AS
(
    SELECT *, 0 AS Generation
    FROM myTable
    WHERE [id] = 99

    UNION ALL
    SELECT name, Generation + 1
    FROM myTable AS Fam
    INNER JOIN FamilyTree
    ON Fam.[id] IN (FamilyTree.[motherid], FamilyTree.[fatherid])
)
SELECT generation, name FROM FamilyTree

【讨论】：