Question

我的oracle版本是10.2。当标量子查询具有聚合操作时，这是非常奇怪的。我的名为t_test的表看起来像这样;

t_id    t_name
 1       1
 2       1
 3       2
 4       2
 5       3
 6       3

查询字符串看起来像这样;

select t1.t_id,
       (select count(t_name)
         from (select t2.t_name 
                 from t_test t2 
                 where t2.t_id=t1.t_id 
                 group by t2.t_name)) a
from t_test t1

此查询的结果是，

这很奇怪，以t1.t_id = 1为例，

select count(t_name)
 from (select t2.t_name 
         from t_test t2 
         where t2.t_id=1
         group by t2.t_name)

结果是1，不知何故，'where'运算符不起作用，结果与我的查询完全相同：

select t1.t_id,
       (select count(t_name)
         from (select t2.t_name 
                 from t_test t2 
                 group by t2.t_name)) a
from t_test t1

为什么？

Answer 1

您是否可以发布SQL * Plus的剪切和粘贴，以准确显示您正在运行的查询？您发布的查询似乎无效 - 别名t1在您引用它的子查询中无效。这让我怀疑你是在简化问题发布在这里，但你不小心把一些重要的东西留了出来。

SQL> ed
Wrote file afiedt.buf

  1  with x as (
  2    select 1 id, 1 name from dual union all
  3    select 2,1 from dual union all
  4    select 3,2 from dual union all
  5    select 4,2 from dual union all
  6    select 5,3 from dual union all
  7    select 6,3 from dual
  8  )
  9  select t1.id
 10        ,(select count(b.name)
 11            from (select t2.name
 12                    from x t2
 13                   where t2.id = t1.id
 14                   group by t2.name) b) a
 15*   from x t1
SQL> /
                 where t2.id = t1.id
                               *
ERROR at line 13:
ORA-00904: "T1"."ID": invalid identifier

据推测，编写这样的查询会更自然（假设你真的想使用标量子查询），其中t1将成为标量子查询中的有效别名。

SQL> ed
Wrote file afiedt.buf

  1  with x as (
  2    select 1 id, 1 name from dual union all
  3    select 2,1 from dual union all
  4    select 3,2 from dual union all
  5    select 4,2 from dual union all
  6    select 5,3 from dual union all
  7    select 6,3 from dual
  8  )
  9  select t1.id
 10        ,(select count(t2.name)
 11            from x t2
 12           where t2.id = t1.id) cnt
 13*   from x t1
SQL> /

        ID        CNT
---------- ----------
         1          1
         2          1
         3          1
         4          1
         5          1
         6          1

6 rows selected.

标量子查询具有聚合操作

1 个答案: