Question

我从查询开始：

SELECT strip.name as strip, character.name as character
  from strips, characters, appearances
 where strips.id = appearances.strip_id
   and characters.id = appearances.character.id
   and appearances.date in (...)

这让我得到了一些结果：

strip                 | character
'Calvin & Hobbes'     | 'Calvin'
'Calvin & Hobbes'     | 'Hobbes'
'Pearls Before Swine' | 'Pig'
'Pearls Before Swine' | 'Rat'
'Pearls Before Swine' | 'Hobbes'  # a guest appearance
'Pearls Before Swine' | 'Calvin'  # a guest appearance

然后我想得到结果集中使用字符（在任何条带中）的次数的COUNT。所以我试过了：

SELECT count(character.id), strip.name as strip, character.name as character
  from strips, characters, appearances
 where strips.id = appearances.strip_id
   and characters.id = appearances.character.id
   and appearances.date in (...)

但那给了我

[ERROR 11:20:17] Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause

所以我试过了：

SELECT count(character.id), strip.name as strip, character.name as character
  from strips, characters, appearances
 where strips.id = appearances.strip_id
   and characters.id = appearances.character.id
   and appearances.date in (...)
 group by character.id

哪个给了我

count | strip                 | character
4     | 'Calvin & Hobbes'     | 'Calvin'
4     | 'Calvin & Hobbes'     | 'Hobbes'
2     | 'Pearls Before Swine' | 'Pig'
2     | 'Pearls Before Swine' | 'Rat'

也就是说，我丢失了所有关于哪些字符出现在哪些条带中的额外信息。

我想得到的是：

count | strip                 | character
4     | 'Calvin & Hobbes'     | 'Calvin'
4     | 'Calvin & Hobbes'     | 'Hobbes'
2     | 'Pearls Before Swine' | 'Pig'
2     | 'Pearls Before Swine' | 'Rat'
4     | 'Pearls Before Swine' | 'Calvin'
4     | 'Pearls Before Swine' | 'Hobbes'

但我似乎无法弄明白。如果重要，我会使用MySQL。也许只需要两次查询。

Answer 1

mySQL是否支持分析功能？像：

SELECT foo.bar, baz.yoo, count(baz.yoo) over (partition by foo.bar) as yoo_count 
from foo, bar
where foo.baz_id = baz.id and baz.id in (...)

可替换地：

SELECT foo.bar, baz.yoo, v.yoo_count 
from foo, bar, 
( select foo.baz_id, count(*) as yoo_count
  from foo
  group by foo.baz_id
) as v
where foo.baz_id = baz.id and baz.id in (...)
and v.baz_id = foo.baz_id;

Answer 2

如何按foo.bar分组？

SELECT count(baz.id) as count, foo.bar, baz.yoo where foo.baz_id = baz.id and baz.id in (...) group by foo.bar

Answer 3

在RDBMS系统上，我将计数查询选择到临时表中，然后将临时表重新加入主表。这将为您提供两全其美的优势。

我不知道mySQL是否支持临时表。

Answer 4

如果MySQL支持分析/窗口功能，则：

select bar, yoo,
    count(yoo) over (partition by yoo) c 
from t
/

否则你需要使用相关的子查询：

select bar, yoo,
    (select count(yoo) from t t2 where t2.yoo=t.yoo) c 
from t
/

在oracle上，测试数据如下：

create table t(bar number, yoo varchar2(16));

insert into t(bar, yoo) values (1, 'hello');

insert into t(bar, yoo) values (2, 'goodbye');

insert into t(bar, yoo) values (3, 'goodbye');

insert into t(bar, yoo) values (4, 'goodbye');

insert into t(bar, yoo) values (2, 'calvin');

insert into t(bar, yoo) values (5, 'Hobbes');

insert into t(bar, yoo) values (6, 'Hobbes');

commit;

Answer 5

子选择：

SELECT foo.bar
    ,baz.yoo
    ,(SELECT COUNT(*) FROM baz AS baz2 WHERE baz2.yoo = baz.yoo etc.) AS yoo_count
FROM foo, baz
WHERE foo.baz_id = baz.id
    AND baz.id in (...)

您也可以进行子选择并将其嵌套并加入。

Answer 6

如果我要合理地要求这样的计数字段，那么我创建一个用户定义的函数来返回值，并在正常选择中使用它。

如何在不丢失查询信息的情况下混合COUNT（）和非COUNT（）列？

6 个答案: