Question

我有一个类似于以下的查询，并且想知道DB2抱怨ORDER BY子句中的关联使用。它错误的像是

[42703] [ - 206]“A.ID”在使用它的上下文中无效。 SQLCODE = -206，SQLSTATE = 42703

我能够重写查询以避免相关用法，但我无法在文档中找到关于此的参考。这是一个错误还是我无法找到预期行为的详细信息？

SELECT a.id
FROM A a
ORDER BY (
  SELECT COUNT(*)
  FROM   B b
  WHERE  b.id = a.id
)

Answer 1

您不能在order by子句中使用相关查询。但是，有很多方法可以获得相同的结果，例如

select count(*) as count_num ,a.ID 
from
   a join  b on  a.ID=b.ID
GROUP BY a.ID
order by 1 DESC

Answer 2

解决方案1：

SELECT a.id, (select count(*) from B where B.id=a.id) nbOFB 
FROM A 
order by 2

Answer 3

解决方案2：

select * from (
SELECT a.id, (select count(*) from B where B.id=a.id) nbOFB 
FROM A
) tmp 
order by nbOFB

Answer 4

解决方案3：

SELECT a.id, c.nb 
FROM A 
inner join lateral
 (
   select count(*) nb from B where B.id=a.id
 ) c on 1=1
order by c.nb

Answer 5

解决方案4：

SELECT a.id, ifnull(c.nb, 0) nb 
FROM A 
left outer join 
(
   select b.id, count(*) nb from B group by b.id
) c on a.id=c.id
order by ifnull(c.nb, 0)

Answer 6

解决方案5：

with c as (
select b.id, count(*) nb from B group by b.id
)
SELECT a.id, ifnull(c.nb, 0) nb 
FROM A left outer join c on a.id=c.id
order by ifnull(c.nb, 0)

DB2中按顺序子句关联的子查询

6 个答案: