Sql 我能在*一个字段*上加一个Where子句吗？

我在一个表中有数据

我可以编写sql来返回每个员工的案例数，如下所示：

select Staff, Count(Staff) as cases
from caseload
group by Staff

select Staff, count(Staff) as oldcases
from caseload
where "Days from lc" >= 21
group by Staff

我还可以编写sql来返回每个员工的旧案例数，如下所示：

select Staff, Count(Staff) as cases
from caseload
group by Staff

select Staff, count(Staff) as oldcases
from caseload
where "Days from lc" >= 21
group by Staff

我的问题是，如何将这两个查询结合起来，得到一个包含三列的结果集：员工、案例、旧案例？每行应包含工作人员姓名、该工作人员的案例数量以及该工作人员超过21天的案例数量

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看起来我应该把where子句放在oldcases字段上，但这不可能是正确的。我知道我缺少一些非常基本的东西。

您可以使用条件聚合：

select Staff, Count(Staff) as cases,
   COUNT(CASE WHEN "Days from lc" >= 21 THEN 1 END) AS oldcases
from caseload
group by Staff;

select Staff, Count(*) as cases,
       sum(case when "Days from lc" >= 21 then 1 else 0 end) as older_cases
from caseload
group by Staff;

---

您可以使用条件聚合：

select Staff, Count(Staff) as cases,
   COUNT(CASE WHEN "Days from lc" >= 21 THEN 1 END) AS oldcases
from caseload
group by Staff;

select Staff, Count(*) as cases,
       sum(case when "Days from lc" >= 21 then 1 else 0 end) as older_cases
from caseload
group by Staff;

---

使用条件聚合：

select Staff, Count(Staff) as cases,
   COUNT(CASE WHEN "Days from lc" >= 21 THEN 1 END) AS oldcases
from caseload
group by Staff;

select Staff, Count(*) as cases,
       sum(case when "Days from lc" >= 21 then 1 else 0 end) as older_cases
from caseload
group by Staff;

---

我不鼓励你用特殊字符来命名专栏。每次引用名称时都必须转义它们是一件麻烦事。

使用条件聚合：

select Staff, Count(Staff) as cases,
   COUNT(CASE WHEN "Days from lc" >= 21 THEN 1 END) AS oldcases
from caseload
group by Staff;

select Staff, Count(*) as cases,
       sum(case when "Days from lc" >= 21 then 1 else 0 end) as older_cases
from caseload
group by Staff;

我不鼓励你用特殊字符来命名专栏。每次你提到这些名字时，都要避开它们是一件麻烦事