Question

我有以下查询返回基本唯一行的最小值，最大值和用户总数在两个不同的表格中。

select sum(user_count) as user_count_sum, sum(min_count) as min_count_sum, 
sum(max_count) as max_count_sum
from(
select max(case when di = 'i' then di_count end) as user_count, 
       min(di_count) as min_count,
       max(di_count) as max_count
from (
    select di, 
           count(distinct rt) as di_count
    from gpstablev2 
    where rt >  GETDATE() - '1 day'::INTERVAL
    group by di
)
UNION
select max(case when di = 'i' then di_count end) as user_count, 
       min(di_count) as min_count,
       max(di_count) as max_count
from (
    select di, 
           count(distinct rt) as di_count
    from powertablev2 
    where rt >  GETDATE() - '1 day'::INTERVAL
    group by di
)
)

现在我还有一个主表，如果我要运行以下查询将返回以下

select table from mastertable;

gpstablev2
powertablev2
...(more table names)

有没有一种方法可以使用查询mastertable清除它，而不是粘贴另外9个UNION块，就像我必须对mastertable中列出的所有表进行求和一样？“ p>

如果我在java中执行此操作，我将首先从主表中获取ResultSet，然后自己执行10次查询和UNION。但我宁愿让我的数据库进行所有处理，并能够根据mastertable的内容进行更新。

编辑：基于反馈我正在尝试动态查询并且已经达到了这个目标，但我仍然无法将其余部分组合在一起

CREATE OR REPLACE FUNCTION get_sums()
RETURNS TABLE(user_count_sum bigint, min_count_sum bigint, max_count_sum bigint)
$BODY$
BEGIN

RETURN QUERY EXECUTE "
SELECT $$SELECT sum(user_count) AS user_count_sum
      ,sum(min_count) AS min_count_sum
      ,sum(max_count) AS max_count_sum
FROM  (
   SELECT max(case when di = 'id' then di_count end) AS user_count
         ,min(di_count) AS min_count
         ,max(di_count) AS max_count
   FROM  ($$
||
string_agg(format($$
      (SELECT di, count(distinct rt) AS di_count
       FROM   %I
       WHERE  rt >  now() - interval '1 day'
       GROUP  BY 1)$$, tbl)
      ,'

      UNION ALL')
|| '
      ) sub1
   ) sub2'
FROM   mastertable;
INTO results_var"

END;
$BODY$
LANGUAGE plpqsql;

Answer 1

您需要动态SQL 。 SQL不接受将文字/值动态转换为标识符。因此，您需要先构建查询然后执行它。您可以在您的客户端（似乎是Java）中执行此操作，或者在Postgres中执行 all ，这通常是最快的：

SELECT $$SELECT sum(user_count) AS user_count_sum
      ,sum(min_count)  AS min_count_sum
      ,sum(max_count)  AS max_count_sum
FROM  (
   ($$
||
string_agg(format($$
   SELECT max(case when di = 'i' then di_count end) AS user_count
         ,min(di_count) AS min_count
         ,max(di_count) AS max_count
   FROM  (
      SELECT di, count(distinct rt) AS di_count
      FROM   %I
      WHERE  rt >  now() - interval '1 day'
      GROUP  BY 1
      ) t
   )$$, tbl)
      ,'

   UNION ALL
   (')
|| '
   ) sub'
FROM   mastertable;

生成查询字符串：

SELECT sum(user_count) AS user_count_sum
      ,sum(min_count)  AS min_count_sum
      ,sum(max_count)  AS max_count_sum
FROM  (
   (
   SELECT max(case when di = 'i' then di_count end) AS user_count
         ,min(di_count) AS min_count
         ,max(di_count) AS max_count
   FROM  (
      SELECT di, count(distinct rt) AS di_count
      FROM   gpstablev2
      WHERE  rt >  now() - interval '1 day'
      GROUP  BY 1
      ) t
   )

   UNION ALL
   (
   SELECT max(case when di = 'i' then di_count end) AS user_count
         ,min(di_count) AS min_count
         ,max(di_count) AS max_count
   FROM  (
      SELECT di, count(distinct rt) AS di_count
      FROM   powertablev2
      WHERE  rt >  now() - interval '1 day'
      GROUP  BY 1
      ) t
   )

   UNION ALL
   ...

   ) sub;

GETDATE()不是有效的Postgres功能。您可能需要now()或CURRENT_DATE ..这取决于未公开的rt类型。我改用 now() 。
您很可能希望在此使用 UNION ALL 而不是UNION。
还修复了子查询中缺少的别名，并进行了一些小的简化。

使用EXECUTE将其包装到 plpgsql 函数中。有plenty of closely related examples here on SO代码，链接和说明......

使用查询结果设置下一个查询的表

1 个答案: