select 时间 , sum(case when 状态='入职' then 1 else 0  end ) as '入职数',
                           sum(case when 状态='离职' then 1 else 0  end ) as '离职数'
from 表
group by  时间

------解决方案--------------------
SQL code

create table tb
(时间 datetime,状态 nvarchar(2))

insert into tb 
select '2012-07-05', '入职' union all
select '2012-07-08', '入职' union all
select '2012-05-03', '离职'

select CONVERT (varchar(7),时间,120) 时间 , 
sum(case when 状态='入职' then 1 else 0  end )  入职人数,
sum(case when 状态='离职' then 1 else 0  end )  离职人数
from tb
group by  CONVERT (varchar(7),时间,120)

------解决方案--------------------
SQL code
if object_id('[TB]') is not null drop table [TB]
go
create table [TB] (时间 datetime,状态 nvarchar(4))
insert into [TB]
select '2012-07-05','入职' union all
select '2012-07-08','入职' union all
select '2012-05-03','离职'

select * from [TB]


SELECT CONVERT(VARCHAR(7),时间,120) AS 时间,
SUM(CASE WHEN 状态 ='入职' THEN 1 ELSE 0 END ) AS '入职人数',
SUM(CASE WHEN 状态 ='离职' THEN 1 ELSE 0 END ) AS '离职人数'
FROM dbo.TB
GROUP BY CONVERT(VARCHAR(7),时间,120)


/*
时间      入职人数        离职人数
------- ----------- -----------
2012-05 0           1
2012-07 2           0

(2 行受影响)

*/

------解决方案--------------------
select '2012-'+convert(varchar(3),MONTH(时间)) as '年月', SUM(case when 状态='入职' then 1 else 0 end)as '入职人数',
sum(case when 状态='离职'  then 1 else 0 end) as '离职人数' from 表名 group by month(时间)


------解决方案--------------------
SQL code

--测试数据
IF OBJECT_ID('[TB]') IS  NOT NULL
DROP TABLE [TB]
GO
CREATE TABLE [TB](DATE datetime,STATUS nvarchar(4))
INSERT INTO [TB]
SELECT '2012-07-05','入职' UNION ALL
SELECT '2012-07-08','入职' UNION ALL
SELECT '2012-05-03','离职'
--SELECT * FROM TB
--开始查询
SELECT CONVERT(VARCHAR(7),DATE,23) AS 时间,
SUM(CASE WHEN STATUS ='入职' THEN 1 ELSE 0 END ) AS '入职人数',
SUM(CASE WHEN STATUS ='离职' THEN 1 ELSE 0 END ) AS '离职人数'
FROM TB
GROUP BY CONVERT(VARCHAR(7),DATE,23)

--查询结果
/*
DATA      入职人数        离职人数
------- ----------- -----------
2012-05 0           1
2012-07 2           0

(2 行受影响)

*/