我有这些 table 。
tb_employee:
ID_EMP NAME_EMP
1 Employee 1
2 Employee 2
3 Employee 3
4 Employee 4
tb_requirements:
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
tb_detail:
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
我需要创建一个SELECT QUERY来计算每个员工有多少需求以及哪种类型，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
我真的不知道该怎么办。
最佳答案
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
关于mysql - 如何从创建虚拟列的表中获取不同的值 'types' - MySQL，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20685861/