非空列在mysql中左移答案

【问题标题】：Not null column to shift left in mysql非空列在mysql中左移
【发布时间】：2013-09-19 19:12:30
【问题描述】：

我正在研究 MySQL 数据库。我有一个表empreporting，这个表包含 employeeid 和 reportingemployeeid 列

SELECT e3.`ReportingEmployeeId` AS Level0,e2.`ReportingEmployeeId` AS Level1,e1.`ReportingEmployeeId` AS Level2,e1.`EmployeeId` AS Level3
FROM empreporting e1
LEFT JOIN empreporting e2 ON e1.`ReportingEmployeeId` = e2.`EmployeeId`
LEFT JOIN empreporting e3 ON e2.`ReportingEmployeeId` = e3.`EmployeeId`

上述查询给出以下结果：

0 级 1 级 2 级 3 级 \N \N 379 369 \N 379 484 372 \N \N \N 379

要求的结果格式是：

0 级 1 级 2 级 3 级 379 369 \N \N 379 484 372 \N 第379章

请任何人帮助我。提前致谢

普拉卡什

【问题讨论】：

标签： mysql sql algorithm

【解决方案1】：

最后写的查询

SELECT 
CASE 
    WHEN e3.`ReportingEmployeeId` IS NOT NULL THEN e3.`ReportingEmployeeId`+1000000 
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NOT NULL THEN e2.`ReportingEmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NOT NULL THEN e1.`ReportingEmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NULL AND e1.`EmployeeId`  IS NOT NULL THEN e1.`EmployeeId` 
END AS Level0,
CASE 
    WHEN e3.`ReportingEmployeeId` IS NOT NULL THEN e2.`ReportingEmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NOT NULL THEN e1.`ReportingEmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NOT NULL THEN e1.`EmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NULL AND e1.`EmployeeId`  IS NOT NULL THEN NULL
END AS Level1,
CASE 
    WHEN e3.`ReportingEmployeeId` IS NOT NULL THEN e1.`ReportingEmployeeId`
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NOT NULL THEN e1.`EmployeeId` 
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NOT NULL THEN NULL
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NULL AND e1.`EmployeeId`  IS NOT NULL THEN NULL
END AS Level2,
CASE
    WHEN e3.`ReportingEmployeeId` IS NOT NULL THEN e1.`EmployeeId` 
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NOT NULL THEN NULL 
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NOT NULL THEN NULL
    WHEN e3.`ReportingEmployeeId` IS NULL AND e2.`ReportingEmployeeId` IS NULL AND e1.`ReportingEmployeeId` IS NULL AND e1.`EmployeeId`  IS NOT NULL THEN NULL
END AS  Level3
FROM empreporting e1
LEFT JOIN empreporting e2 ON e1.`ReportingEmployeeId` = e2.`EmployeeId` 
LEFT JOIN empreporting e3 ON e2.`ReportingEmployeeId` = e3.`EmployeeId`

【讨论】：

...那么 e3.ReportingEmployeeId+1000000？那个是从哪里来的？如果没有其他原因，除了你把它全部写出来之外，也可以投票。

【解决方案2】：

试试

SELECT e1.EmployeeId AS Level0,e2.`EmployeeId` AS Level1,e3.`EmployeeId` AS Level2,e3.`ReportingEmployeeId` AS Level3
FROM empreporting e1
LEFT JOIN empreporting e2 ON e1.`ReportingEmployeeId` = e2.`EmployeeId`
LEFT JOIN empreporting e3 ON e2.`ReportingEmployeeId` = e3.`EmployeeId`

【讨论】：

感谢您的快速回复.. :)