Question

我有一个类似以下的查询，但没有工作：

SELECT  COUNT(*) as count,  a.COUNT(*) AS total
FROM A
WHERE key IN  (SELECT key
                FROM B
                WHERE condition
               ) a
GROUP BY key;

我也希望得到总数结果

(SELECT key
 FROM B
 WHERE condition
)

我如何给它贴上标签，并在外部选择中使用它？还是其他任何方法？感谢？

Answer 1

您正在寻找的是Left Join

SELECT a.key, sum(b.bCount) as count,  a.COUNT(*) AS total
FROM A
LEFT JOIN  (
   SELECT key, COUNT(1) as bCount
   FROM B
   WHERE condition
) b
on A.key = b.key
GROUP BY key;

Answer 2

如果我正确理解你的目标：

with 
  a1 as (select key, count(*) as cnt from a group by key),
  b1 as (select key, count(*) as cnt from b where condition group by key)
select
  a1.key, a1.cnt, b1.cnt
from
  a1 join b1 on (a1.key = b1.key)

Answer 3

在PG identifiers are case-insensitive中。因此，在您的查询表中A和子查询a与服务器是相同的，这是不可能的。实际上，即使您执行了a，该表也可能被称为CREATE TABLE A (...)。只有在创建时双引号表名称（例如"A"），才会保留该案例，但是您还应该在所有查询中双引号表名称。为子查询提供不同的标签或双引表名将使错误消失。

在您的子查询中，如果您希望主查询中提供该信息，则需要进行计数。而不是相关的子查询 - key IN ... - 您应该进行两个子查询（因为它们分组可能不同的不同关系）并在主查询中JOIN：

SELECT key, sub1.count, sub2.total
FROM (
  SELECT key, count(*) AS count FROM a
  GROUP BY key ) sub1
JOIN (
  SELECT key, count(*) AS total FROM b
  WHERE condition
  GROUP BY key ) sub2 USING (key);

如何为子查询命名

3 个答案: