Question

我有一张看起来像这样的表：

     ID    |     STATUS    |     TYPE
----------------------------------------
x123       |      A        | High School
x122       |      I        | High School
x124       |      F        | High School
x125       |      A        | College
x126       |      I        | College
x127       |      F        | College
x128       |      F        | College

任何人都可以帮我提出一个oracle 8i的查询，它会像这样显示这个表

Type             |    Count A    |    Count I    |  Count F
------------------------------------------------------------
High School      |     1         |     1         |  1
College          |     1         |     1         |  2

谢谢！

Answer 1

这是一种方法：

select t.type                                          as "Type"
     , sum(case when t.status = 'A' then 1 else 0 end) as "Count A"
     , sum(case when t.status = 'I' then 1 else 0 end) as "Count I"
     , sum(case when t.status = 'F' then 1 else 0 end) as "Count F"
  from my_table t
 group by t.type
 order by t.type desc

如果您要返回特定列，则此方法有效，并且可以“计算”符合更复杂条件集的行。

[编辑]

（添加了DESC关键字以获得如OP所示的排序结果集，Rob van Wijk获得+1好抓！）

（Andomar做了一个很好的观察，在结果集中有越来越多的列，使用这种方法，语句变得不合适。还有其他方法来获得相同的结果集，如果唯一的“测试”是一个单列上的等式比较。）

Oracle 8i确实支持CASE表达式，不是吗？如果我没记错的话，Oracle 8没有。我们可以通过DECODE函数去“老学校”做同样的事情：

select t.type                        as "Type"
     , sum(decode(t.status,'A',1,0)) as "Count A"
     , sum(decode(t.status,'I',1,0)) as "Count I"
     , sum(decode(t.status,'F',1,0)) as "Count F"
  from my_table t
 group by t.type
 order by t.type DESC

[/编辑]

有时，我们要检查多个类型条件，并在多个计数中包含一行。我们可以得到一个总数

select t.type                                             as "Type"
     , sum(case when t.status in ('A') then 1 else 0 end) as "Count A"
     , sum(case when t.status in ('I') then 1 else 0 end) as "Count I"
     , sum(case when t.status in ('F') then 1 else 0 end) as "Count F"
     , sum(case when t.status in ('A','I') then 1 else 0 end) as "#AI"
     , sum(decode(sign(t.foo-t.bar),1,1,0))               as "#foo>bar"
     , sum(decode(sign(10.0-t.foo),1,1,0))                as "#foo<10"
  from my_table t
 group by t.type
 order by t.type desc

（只是要指出，一行可能满足多列的指定条件，因此可以多次“计数”。有时，这正是我们想要的。）

Oracle 8i查询帮助

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