如何将 Select 中不同表中的两个值相除

Question

我需要划分两个表，nr1 和 nr2，如下所示

SELECT COUNT(candidate.id) as nr1
FROM candidate
WHERE candidate.id=2



select count (candidate.id) as nr2
from candidate 
where candidate.id=2 or candidate.id = 3;

select nr1/nr2 from nr1, nr2;

问题是它们不存在于 select 查询之外。

Answer 1

在 oracle 中你可以创建一个 cte。

With table1 as ( 
      SELECT COUNT(candidate.id) as nr1
      FROM candidate
      WHERE candidate.id=2
), 
table2 as (
     select count (candidate.id) as nr2
     from candidate 
     where candidate.id=2 or candidate.id = 3
)
SELECT table1.nr1 / table2.nr2
FROM table1
CROSS JOIN table2

但是一个简单的方法应该是使用条件 SUM，你还必须验证 div 0 个案例。

WITH cte AS (
  SELECT         
       SUM(CASE WHEN candidate.id = 2 THEN 1 ELSE 0 END) as nr1,          
       SUM(CASE WHEN candidate.id IN (2,3) THEN 1 ELSE 0 END) as nr2
  FROM candidate
)
SELECT (CASE WHEN nr2 > 0 THEN nr1 / nr2 END) as result
FROM cte

Answer 2

您可以在单个查询中完成。 Aggregate 有条件地 SELECT 中的数据。

SELECT COUNT(CASE WHEN id = 2  THEN 1 END) 
       / COUNT(CASE WHEN id = 2 || id = 3 THEN 1 END) 
FROM candidate

Answer 3

我会使用条件聚合来解决这个问题：

select (sum(case when c.id = 2 then 1.0 else 0 end) /
        sum(case when c.id in (2, 3) then 1.0 else 0 end)
       ) 
from candidate;

如何将 Select 中不同表中的两个值相除

How To Divide Two Values From Different Tables in Select

sql

oracle

oracle12c