将多个联接合并到一个选择/案例中

Question

我目前正在使用不同的条件查询一个表 4 次，然后使用左连接作为更大查询的一部分来返回所有数据。较大的查询运行速度不是特别快，我相当肯定我当前的方法效率不高。

我想知道是否有可能以某种方式使用 CASE 语句来增加 4 列之一。我目前的 4 个查询是：

SELECT ts.department, 
                         Sum([hours]) AS ChargeableTimeYTD 
                  FROM   bwbfiles.sos.timesummary ts 
                  WHERE  category = 'C' 
                         AND [year] = '2019' 
                  GROUP  BY department


SELECT ts.department, 
                         Sum([hours]) AS ChargeableTimeMTD 
                  FROM   bwbfiles.sos.timesummary ts 
                  WHERE  category = 'C' 
                         AND [year] = '2019' 
                         AND [period] = 4 
                  GROUP  BY department


SELECT ts.department, 
                         Sum([hours]) AS NonChargeableTimeProBono 
                  FROM   bwbfiles.sos.timesummary ts 
                  WHERE  category = 'NC' 
                         AND ( [act_code] = '001N' 
                                OR [act_code] = '00N6' ) 
                         AND [year] = '2019' 
                  GROUP  BY department


SELECT ts.department, 
                         Sum([hours]) AS NonChargeableTimeNonProBono 
                  FROM   bwbfiles.sos.timesummary ts 
                  WHERE  category = 'NC' 
                         AND ( [act_code] <> '001N' 
                               AND [act_code] <> '00N6' ) 
                         AND [year] = '2019' 
                  GROUP  BY department

目标是最终得到一个包含 5 列的查询结果 部门、ChargeableTimeYTD、ChargeableTimeMTD、NonChargeableTimeProBono、NonChargeableTimeNonProBono

或者我会从每个位中按部门删除分组而不是 CASE，并有一个生成 3 列的查询

Department、Hours、Category（其中 Category 是 ChargeableTimeYTD/ChargeableTimeMTD 等...等等），然后将其转为 5 列。

提前致谢！

Answer 1

这可能会满足您的要求

SELECT ts.department, 
    Sum(case when category = 'C' then [hours] else 0 end) AS ChargeableTimeYTD,
    Sum(case when category = 'C' and [period] = 4 then [hours] else 0 end) AS ChargeableTimeMTD,
    Sum(case when category = 'NC' and ([act_code] = '001N' or [act_code] = '00N6') then [hours] else 0 end) AS NonChargeableTimeProBono,
    Sum(case when category = 'NC' and ([act_code] <> '001N' or [act_code] <> '00N6') then [hours] else 0 end) AS NonChargeableTimeNonProBono
FROM   bwbfiles.sos.timesummary ts 
where [year] = '2019'
and [category] in ('C','NC')
GROUP  BY department