Question

我正在尝试使用CASE语句编写postgres查询。查询如下：

SELECT "State" AS x, count("Age Group") AS y from test.smp_state_survey where "State" IN 
(CASE 
        WHEN 'State' = 'State' THEN 'State 1','State 2','State 3'
        WHEN 'State' = 'District' THEN 'State 1'
    END) 
  group by x ORDER BY x,y

以上查询显示'State' = 'State'

处的语法错误

然而，当我执行以下查询时，我得到了适当的结果：

SELECT "State" AS x, count("Age Group") AS y from test.smp_state_survey where "State" IN 
(CASE 
        WHEN 'State' = 'State' THEN 'State 1'
        WHEN 'State' = 'District' THEN 'State 1'
    END) 
  group by x ORDER BY x,y

请让我知道我做错了什么。

修改

THEN子句后面的值是动态的，它可能包含一个或多个值（来自多选框）。我希望查询以

的形式执行

SELECT "State" AS x, count("Age Group") AS y from test.smp_state_survey where "State" IN 
('State 1','State 2','State 3') 
  group by x ORDER BY x,y

哪个运行得很好，但问题是CASE没有返回我所需的字符串。

Answer 1

您的查询应该是这样的，我希望这对您有用

SELECT  "State" AS x, count("Age Group") AS y from test.smp_state_survey where  
CASE  
        WHEN 'State' = 'State'  THEN  "State" IN  ('State 1' ,'State 3')
        WHEN 'State' = 'District' THEN "State" IN  ('District 1')
    END
  group by x ORDER BY x,y

Answer 2

'州'='州'是同义反复。你的意思是“State”='State'，即“State”列的值等于字符串'State'吗？

Answer 3

由于您尝试使用IN，因此您可以利用IN接受集合或数组这一事实：

SELECT "State" AS x, count("Age Group") AS y
FROM test.smp_state_survey
WHERE "State" IN (CASE
  WHEN 'State' = 'State' THEN ARRAY['State 1','State 2','State 3']
  WHEN 'State' = 'District' THEN ARRAY['State 1']
END) 
GROUP BY x
ORDER BY x,y

或使用@ user1327246的重新措辞，将IN测试推送到CASE语句。

Answer 4

单个案例不能有多个值。

这就是问题

WHEN 'State' = 'State' THEN 'State 1','State 2','State 3'

Postgres案例查询问题

4 个答案: