查找计数发生次数

Question

我有一个包含2列的表（db：sql server 2008）：

id         name
-----      ------
1          Bob
2          Mike
3          Mary
4          Mike
5          Barry
6          Benson
7          Burrows

我想得到一个以B开头并以M开头的名字（一行）？

像：

Count of B        Count of M
-----------      ------------
4                  3

唯一能给我的是工会。任何想法在单个查询中更清洁（没有联合）？

Answer 1

使用CASE，

尝试

SELECT  SUM(CASE WHEN SUBSTRING(name,1,1) = 'B' Then 1 ELSE 0 END),
        SUM(CASE WHEN SUBSTRING(name,1,1) = 'M' Then 1 ELSE 0 END)
FROM TAbleName

SQLFiddle Demo

Answer 2

您可以使用PIVOT。如果您有已知数量的列，则可以使用STATIC PIVOT：

对值进行硬编码

select *
from
(
  select substring(name, 1, 1) name, -- use the same field twice, 
    substring(name, 1, 1) initial    -- once will be for the count the other for columns
  from yourtable
) x
pivot
(
  count(name)
  for initial in ([B], [M])
) p

请参阅SQL Fiddle With Demo

如果要转换的列数未知，则可以使用动态sql并创建动态PIVOT：

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT distinct ',' 
                      + QUOTENAME(substring(name, 1, 1)) 
                    from yourtable
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT ' + @cols + ' from 
             (
              select substring(name, 1, 1) name, 
                substring(name, 1, 1) initial
              from yourtable
            ) x
            pivot 
            (
                count(name)
                for initial in (' + @cols + ')
            ) p '

execute(@query)

请参阅SQL Fiddle with Demo

如果您希望将数据集过滤到仅以B or M开头的数据集，那么您可以使用WHERE子句进行过滤。

where substring(name, 1, 1) in ('B', 'M')

Answer 3

这是另一种方式

Declare @T Table ([id] varchar(5), [name] varchar(7));

INSERT INTO @T([id], [name])
VALUES
    ('1', 'Bob'),
    ('2', 'Mike'),
    ('3', 'Mary'),
    ('4', 'Mike'),
    ('5', 'Barry'),
    ('6', 'Benson'),
    ('7', 'Burrows')

;WITH CTE AS
(SELECT
    Initials = SUBSTRING(name,1,1)
    ,Cnt = COUNT([name]) 
FROM @t 
GROUP BY SUBSTRING(name,1,1))

SELECT 
    [Count of B] = (SELECT Cnt FROM CTE WHERE Initials = 'B')
    ,[Count of M] = (SELECT Cnt FROM CTE WHERE Initials = 'M')

<强>结果

Count of B  Count of M
4             3