数据库 sql 学习笔记

1.trim ()

https://blog.csdn.net/u012630060/article/details/71367537

 2.left join

https://blog.csdn.net/traceofsun/article/details/6074856

3.union和union all

https://www.cnblogs.com/mzhaox/p/11204767.html

4.order by 

https://www.jianshu.com/p/2b21a0f564f8

5.INTO

https://blog.csdn.net/VALUETOME111/article/details/62042232?depth_1-

6.group by

https://blog.csdn.net/s00229295/article/details/96041555

7.sum (case when   then   else  end  )

 https://segmentfault.com/a/1190000020877471

8.for update

https://www.cnblogs.com/banma/p/11797560.html