Oracle 主从表联合查询
表A
id type name
1 E AA
2 F


表B
id Aid name
1 2 BB
2 2 CC

表B 是表A的子表
如果表A中的type是F，就需要根据Aid 去表B里找对应的name，然后拼接起来

数据库是Oracle10G 需要查询的结果：

Aid type name
1 E AA
2 F BB,CC
[最优解释]

 with a as(
 select 1 id,'E' type,'AA' name from dual
 union all
 select 2,'F',null from dual
 ),b as(
 select 1 id, 2 aid, 'BB' name from dual
 union all
 select 2,2,'CC' from dual
 )
 select a.id, a.type, wm_concat(nvl(a.name, b.name))
   from a, b
  where a.id = b.aid(+)
  group by a.id, a.type;
        ID TYPE WM_CONCAT(NVL(A.NAME,B.NAME))
---------- ---- --------------------------------------------
         1 E    AA
         2 F    BB,CC

WITH TABLE1 AS(
      SELECT '1' AS Aid, 'E' AS type,'AA' as name FROM dual
      union all     
      SELECT '2' AS Aid, 'F' AS type,'' as name FROM dual
      union all     
      SELECT '3' AS Aid, 'F' AS type,'' as name FROM dual
      union all     
      SELECT '4' AS Aid, 'A' AS type,'FF' as name FROM dual
),
TABLE2 AS (    
      SELECT '1' AS id, '2' AS Aid,'BB' as name FROM dual
      union all     
      SELECT '2' AS id, '2' AS Aid,'CC' as name FROM dual
      union all  
      SELECT '3' AS id, '3' AS Aid,'DD' as name FROM dual
      union all     
      SELECT '4' AS id, '3' AS Aid,'EE' as name FROM dual
)
 
SELECT T1.Aid,
       T1.TYPE,
       LISTAGG(nvl(T1.NAME, T2.NAME),',')WITHIN GROUP(ORDER BY id) AS NAME 
 
  FROM TABLE1 T1
  LEFT JOIN TABLE2 T2 ON T1.Aid = T2.Aid
 GROUP BY T1.Aid, T1.TYPE

 SELECT T1.NAME 
[其他解释]
由于查询的字段很多   能否不用 【GROUP BY】
用函数实现也可以