SQL Count（）列值

Question

我有以下源表：

pid | code
----------
1      P2
2      P2
3      P3
4      P1
5      P2
6      P1

现在，我想获取每个代码存在多少次的信息：

code | count
------------
P2      3
P1      2
P3      1

所以我想计算代码列中的值并将其分配给不同的可用代码值集。最后，我想按计数编号。

Answer 1

SQL Fiddle：

SELECT t.code, COUNT(*) AS `count`
FROM MyTable t
GROUP BY t.code
ORDER BY COUNT(*) DESC

Answer 2

DECLARE @testTable table (pid  int
                     ,code varchar(2)
)

insert into @testTable values (1, 'P2')
insert into @testTable values (2, 'P2')
insert into @testTable values (3, 'P3')
insert into @testTable values (4, 'P1')
insert into @testTable values (5, 'P2')
insert into @testTable values (6, 'P1')


SELECT CODE, COUNT(1) AS [COUNT]
FROM @testTable 
GROUP BY CODE
ORDER BY [COUNT] DESC