基于最大相关行数的子查询

Question

我正在使用 Oracle 11g R2。

我想 return 来自具有多个子行的 table 的单个值。子查询必须 return 基于第二个不相关列的最大值数的值。

以下代码以 CTE 的形式提供数据...以及创建语句的失败尝试。我知道我必须以某种方式区分这些值，以便它 return 是拥有最大子数量的值。

检查片段 "Expected result"。

WITH GRPS(GRP, SUBGRP)
AS
(
    SELECT 'AAA', 'SUB_A1' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A3' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B5' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B6' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B6' FROM DUAL UNION ALL 
    SELECT 'BBB', 'SUB_B7' FROM DUAL 
),
TAB1 (GRP)
AS
(
   SELECT 'AAA' FROM DUAL UNION ALL
   SELECT 'BBB' FROM DUAL 
)

(


SELECT 
    TAB1.GRP,
    GRPS.SUBGRP, 
    COUNT(*)
FROM TAB1
JOIN GRPS 
    ON (GRPS.GRP = TAB1.GRP)
GROUP BY TAB1.GRP,
GRPS.SUBGRP 

-- That will get me these:
-- Row# GRP SUBGRP COUNT(*)
-- 1 BBB SUB_B5 1
-- 2 AAA SUB_A2 3
-- 3 AAA SUB_A1 1
-- 4 BBB SUB_B6 2
-- From which I still have to perform a search to get me the rows with SUB_B6 AND SUB_A2


-- Expected result
-- AAA SUB_A2
-- BBB SUB_B6

)
;

这当然不会起作用，并且会给我一个像 "single-row subquery returns more than one row" 这样的错误。我不需要从相关子查询中获取任何行。我需要从 table 中获取重复次数更多的值。在这种情况下 SUB_A2，并且 SUB_B6。

Answer 1

使用Analytic Function。试试这个

WITH GRPS(GRP, SUBGRP)
AS
(
    SELECT 'AAA', 'SUB_A1' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'AAA', 'SUB_A2' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B5' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B6' FROM DUAL UNION ALL
    SELECT 'BBB', 'SUB_B6' FROM DUAL 
),
TAB1 (GRP)
AS
(
   SELECT 'AAA' FROM DUAL UNION ALL
   SELECT 'BBB' FROM DUAL 
)

(

select grp,subgrp from(
SELECT 
    TAB1.GRP,
    GRPS.SUBGRP, 
    row_number() over(partition by TAB1.GRP order by  count(1) desc) rn
FROM TAB1
JOIN GRPS 
    ON (GRPS.GRP = TAB1.GRP)
  group by TAB1.GRP,
    GRPS.SUBGRP
) a where rn=1
)
;

基于最大相关行数的子查询

Subquery based on max number of related rows

sql

oracle

oracle11g

FIDDLE DEMO