一.截断字符串
declare @str varchar(100)
set @str='123456'
print substring(@str,1,5); 从1的前面算起截取长度为5的字符串
print substring(@str,1,5);从1算起截取长度为5的字符串
print left(@str,5) 从左边开始截取
print right(@str,5)
print ltrim(@str); 去掉字符串左边的空格
print rtrim(@str)
二.not 的用法
select * from table where column not in ('a','b','c')
not和between连用时要紧跟在where的后面
select * from table where not column between 10 and 30
not和or 、and连用时要紧跟在它们后面
select * from table where not column like '%a' and not column2 like '%b'
三.分组并算出各分组的合计、平均值、max、min、count
select Username ,sum(number) as a from table group by Username
select Username ,avg(number) as a from table group by Username
select count(distinct sale_date) from cook_sales
对不同用户的number做合计，然后再按合计数据大小排序
select Username ,sum(number) as a from table group by Username order by sum(number) desc
四.inner join、left join 、right join、full join
student：
class：
inner join(内连接)
方法一
select * from student as s,class as c where s.classid=c.classid
方法二
select * from student as s inner join class c on s.classid=c.classid
select * from student as s inner join class c on s.classid<>c.classid
left join(左连接)
select * from student as s left join class c on s.classid=c.classid
right join(右连接)
select * from student as s right join class c on s.classid=c.classid
full join(全连接)
select * from student as s full join class c on s.classid=c.classid
cross join（交叉连接）
select * from student as s cross join class c
select * from student as s ,class c
条件查询
select * from student as s cross join class c where s.classid=c.classid
select * from student as s , class c where s.classid=c.classid
(cross join 后的条件只能用where)
五、数据类型转换
select CONVERT(int, 12.1)
select CONVERT(int, '12.1') 报错
select CONVERT(int, convert(decimal(8,1),'12.1')) 正确
select CONVERT(varchar(200),GETDATE(),120) 获取当前时间、设置格式、以字符串形式输出
六、sql拼接并去重列值
select( select distinct CAST(F_ModuleName as varchar)+',' from Sys_Log where F_ModuleName!='' for xml path('') ) as A
第4段这一部分是参考作者：于亮的博客
在此感谢他，谢谢分享