鉴于这些表格...
CREATE TABLE tblEmployees (
EmployeeID SMALLINT,
ReportsTo SMALLINT,
IsBigBoss BIT);
CREATE TABLE tblTargetEmployees (
EmployeeID SMALLINT);
INSERT INTO tblEmployees VALUES
(1,NULL,NULL),
(2,1,1),
(3,1,1),
(4,1,1),
(5,1,1),
(6,2,0),
(7,6,0),
(8,6,0),
(9,3,0),
(10,4,0),
(11,10,0),
(12,10,0),
(13,5,0),
(14,2,0),
(15,10,0);
INSERT INTO tblTargetEmployees VALUES
(8),
(9),
(10),
(11),
(12),
(14);
这个查询...
WITH cte AS (
SELECT e.EmployeeID, BigBossID=e.EmployeeID, e.ReportsTo
FROM tblEmployees e
WHERE e.IsBigBoss=1
UNION all
SELECT e.EmployeeID, cte.BigBossID, e.ReportsTo
FROM tblEmployees e
JOIN cte ON e.ReportsTo=cte.EmployeeID
)
SELECT *
FROM cte
WHERE EXISTS (SELECT * FROM tblTargetEmployees te WHERE te.EmployeeID=cte.EmployeeID)
ORDER by EmployeeID
我得到了预期的结果。我的目标表中的所有六名员工均已返回。但是,如果我将过滤器移至 cte,则会删除一名员工 (#8)。
WITH cte AS (
SELECT e.EmployeeID, BigBossID=e.EmployeeID, e.ReportsTo
FROM tblEmployees e
WHERE e.IsBigBoss=1
UNION all
SELECT e.EmployeeID, cte.BigBossID, e.ReportsTo
FROM tblEmployees e
JOIN cte ON e.ReportsTo=cte.EmployeeID
WHERE EXISTS (SELECT * FROM tblTargetEmployees te WHERE te.EmployeeID=e.EmployeeID)
)
SELECT *
FROM cte
ORDER by EmployeeID
现在,我明白了为什么当我将过滤器移至 cte 时会遇到额外的“Big Boss”行,但我很难理解为什么 employeeID 8 被过滤掉。
非常感谢任何帮助我用简单的头脑来理解这种行为的帮助。
最佳答案
因为 EmployeeId 6 不存在于 tblTargetEmployees 中,所以当它进入递归并开始添加员工 id 6 时,它会查找它是否存在于 tblTargetEmployees 表中。如果并且永远不会到达员工 ID 8,则递归行不会停止。
所以要使用数据
- 2 是 bigboss,并在 anchor 表中表示
- 6 是直接 boss,但不存在,因此之后不会再次调用递归。
- 8正在等待被发现......
将 WHERE 语句移出 cte,您将看到所需的结果
;WITH cte AS (
SELECT e.EmployeeID, BigBossID=e.EmployeeID, e.ReportsTo
FROM tblEmployees e
WHERE e.IsBigBoss=1
UNION all
SELECT e.EmployeeID, cte.BigBossID, e.ReportsTo
FROM tblEmployees e
JOIN cte ON e.ReportsTo=cte.EmployeeID
)
SELECT *
FROM cte e
WHERE EXISTS (SELECT * FROM tblTargetEmployees te WHERE te.EmployeeID=e.EmployeeID)
ORDER by EmployeeID
关于SQL Server 递归 CTE - 为什么会出现这种行为?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/38274983/