SQL查询多个SUM函数

Question

我在MySql中有三个表

T1

budgetId    fin_year
---------------------
1           17-18

T2

divisionId  budgetId    totalAmount
-----------------------------------
1           1           10000
2           1           10000
3           1           10000
4           1           0
5           1           100

T3

workId  divisionId  budgetId    workDescription     workAmount
--------------------------------------------------------------
1       1           1           sssdfs              500
2       1           1           fsfcdsdfgfd         200

现在我希望T2表的 totalAmount 的总和以及相同budgetId的 T3的总WorkAmount 的总和

Answer 1

尝试以下查询。

select sum(totalAmount) as total , budgetId , sum(workAmount) as total_used  from T2 
Left Join T3 on T3.budgetId = T2.budgetId
Group By budgetId

希望此查询对您有所帮助，如果您收到任何错误，请告诉我。

Answer 2

如果您只是进行联接和每列的总和，那么您可能会遇到的问题可能会夸大您的预算金额。如果您有多个工作ID（T3），那么T2将为每个ID求和。您最好通过预算ID对T2和T3表进行一次预先求和并加入其中。这可以防止笛卡尔结果问题。

select
      T1.fin_Year,
      T2Sum.BudgetID,
      T2Sum.TotalByBudget,
      coalesce( T3Sum.WorkAmtPerBudget, 0.0 ) as WorkPerBudget
   from
      T1
         JOIN
         ( select
                 budgetID,
                 sum( totalAmount ) TotalByBudget
              from
                 T2
              group by
                 budgetID ) T2Sum
            on T1.budgetID = T2Sum.budgetID
            LEFT JOIN
            ( select 
                    budgetID,
                    sum( workAmount ) WorkAmtPerBudget
                 from
                    T3
                 group by
                    budgetID ) T3Sum
              on T2Sum.BudgetID = T3Sum.BudgetID