Question

SELECT 'table_1' as FlowStepCount, COUNT(fs.ID)  
FROM [FlowSteps] fs
where fs.FlowID = 120
UNION all
SELECT 'table_2' as FlowStepAssignmentCount, COUNT(fsa.ID)  
FROM [FlowStepAssignments] fsa
where fsa.FlowStepID IN (select ID from [FlowSteps] where FlowID = 120)

我想显示如下查询：

FlowStepCount   FlowStepAssignmentCount
18              64

我还希望将FLOW表的ID加入FLOWSTEP表的FlowID。我试图加入3表但无法解决它。

我实际上想写这样的查询：

SELECT 
   count(fs.ID) as FlowStepCount, 
   count(fsa.ID) as FlowStepAssignmentCount
FROM
   [Flow] f, 
   [FlowSteps] fs,
   [FlowStepAssignments] fsa
WHERE      
   fs.ID = fsa.FlowStepID AND
   f.ID = fs.FlowID AND
   f.ID = 120

有什么建议吗？如何加入3个表并获取它们的计数（*）只是给出FlowID？

Answer 1

这可以解决您的问题：

SELECT count(distinct fs.ID) as FlowStepCount, 
       count(distinct fsa.ID) as FlowStepAssignmentCount
FROM [Flow] f left join 
     [FlowSteps] fs
     on f.ID = fs.FlowID left join
     [FlowStepAssignments] fsa
     on fs.ID = fsa.FlowStepID
WHERE f.ID = 120;

通常使用子查询的方式更有效：

select (select count(*) from FlowSteps fs where f.ID = fs.FlowID) as FlowStepCount,
       (select count(*) from FlowStepAssignments fsa where f.ID = fsa.FlowID) as FlowStepAssignmentCount,

from Flow f
where f.id = 120;

从多个表中选择行计数

1 个答案: