如何获得不同的值'；类型'；从表创建虚拟列-MySQL

我有这些桌子

tb\U员工：

ID_EMP           NAME_EMP
1               Employee 1
2               Employee 2
3               Employee 3
4               Employee 4

ID_REQ                  DESCRIPTION_REQ               TYPE_REQ
1                        Requirement 1                   1
2                        Requirement 2                   1
3                        Requirement 3                   1
4                        Requirement 4                   2
5                        Requirement 5                   2
6                        Requirement 6                   2
7                        Requirement 7                   2

ID_DET                        ID_EMP                        ID_REQ
1                               1                             1
2                               1                             2
3                               1                             4
4                               2                             1
5                               2                             6
6                               3                             4
7                               3                             7

tb\U要求：

ID_EMP           NAME_EMP
1               Employee 1
2               Employee 2
3               Employee 3
4               Employee 4

ID_REQ                  DESCRIPTION_REQ               TYPE_REQ
1                        Requirement 1                   1
2                        Requirement 2                   1
3                        Requirement 3                   1
4                        Requirement 4                   2
5                        Requirement 5                   2
6                        Requirement 6                   2
7                        Requirement 7                   2

ID_DET                        ID_EMP                        ID_REQ
1                               1                             1
2                               1                             2
3                               1                             4
4                               2                             1
5                               2                             6
6                               3                             4
7                               3                             7

tb\U详细信息：

ID_EMP           NAME_EMP
1               Employee 1
2               Employee 2
3               Employee 3
4               Employee 4

ID_REQ                  DESCRIPTION_REQ               TYPE_REQ
1                        Requirement 1                   1
2                        Requirement 2                   1
3                        Requirement 3                   1
4                        Requirement 4                   2
5                        Requirement 5                   2
6                        Requirement 6                   2
7                        Requirement 7                   2

ID_DET                        ID_EMP                        ID_REQ
1                               1                             1
2                               1                             2
3                               1                             4
4                               2                             1
5                               2                             6
6                               3                             4
7                               3                             7

我需要做一个

选择查询

来计算每个员工有多少

需求

以及哪些类型，如下所示：

ID_EMP               NAME_EMP          TYPE_REQ1(virtual column)     TYPE_REQ2 (virt. c.)
1                    Employee 1               2                         4
2                    Employee 2               1                         1
3                    Employee 3               0                         2
4                    Employee 4               0                         0

我真的不知道怎么做。

试试这个

SELECT 
e.ID_EMP 
,e.NAME_EMP
,(CASE WHEN SUM(r.TYPE_REQ=1) IS NULL THEN 0 ELSE SUM(r.TYPE_REQ=1) END ) TYPE_REQ1
,(CASE WHEN SUM(r.TYPE_REQ=2) IS NULL THEN 0 ELSE SUM(r.TYPE_REQ=2) END ) TYPE_REQ2
FROM 
tb_employee e
LEFT JOIN tb_detail d ON (e.ID_EMP=d.ID_EMP)
LEFT JOIN  tb_requirements r ON (d.ID_REQ=r.ID_REQ)
GROUP BY e.ID_EMP

---

太棒了！但是，这仅显示第一名员工的“详细信息”（在本例中为

ID\u EMP 1

）。。。我将尝试修改query@JhonatanSandoval看到我的更新答案与左joinGREAT！！但是现在我在某些行中看到

NULL

，如何将其设置为

0

？我记得好像

是空的（总和…

？很好！！谢谢你的帮助！适当的DDL和/或SQLFIDLE以及所需的结果集可能会有所帮助