提高查询在PostgreSQL中

Question

我需要改善查询PostgreSQL中

select a.* 
      ,(select num 
        from TABLEA c 
       where c.one = a.one 
        and c.two = a.two 
        and c.three = a.three 
        and c.four= a.four 
        and c.five = 'A') as A 
      ,(select num 
        from TABLEA c 
       where c.one = a.one 
        and c.two = a.two 
        and c.three = a.three 
        and c.four = a.four 
        and c.five = 'B') as B 
      ,(select num 
        from TABLEA c 
       where c.one = a.one 
        and c.two = a.two 
        and c.three = a.three 
        and c.four = a.four 
        and c.five = 'C') as C 
       from TABLEB a 

我想只运行一个选择来获得A，B，C ....

Answer 1

我想你可以试试这个：

SELECT A.*, 
     C.A, C.B, C.C 
FROM TABLEB A 
LEFT JOIN (
    SELECT one, two, three, four 
     , MAX(CASE WHEN five = 'A' THEN num ELSE NULL END) AS A 
     , MAX(CASE WHEN five = 'B' THEN num ELSE NULL END) AS B 
     , MAX(CASE WHEN five = 'C' THEN num ELSE NULL END) AS C 
    FROM TABLEA 
    WHERE five IN ('A','B','C') 
    GROUP BY one, two, three, four 
) C ON c.one = a.one 
        and c.two = a.two 
        and c.three = a.three 
        and c.four= a.four; 

输出：

one two three four a  b c 
1 1 2 3  4  10  20 30 
2 5 6 7  8  NULL 100 NULL 

Answer 2

尝试这样的：

select 
(CASE WHEN five = 'A' THEN num ELSE NULL END), 
(CASE WHEN five = 'B' THEN num ELSE NULL END), 
(CASE WHEN five = 'C' THEN num ELSE NULL END) 
from TABLEA