select * from 表 where id > 1 and name != ‘alex‘ and num = 12;
select * from 表 where id between 5 and 16;
select * from 表 where id in (11,22,33)
select * from 表 where id not in (11,22,33)
select * from 表 where id in (select nid from 表)

select * from 表 where name like ‘liu%‘  # liu开头的所有（多个字符串）
select * from 表 where name like ‘liu_‘  #liu开头的所有（一个字符）
select * from 表 where name like ‘%liu_‘
select * from 表 where name like ‘_liu_‘
select * from 表 where name like ‘%liu%‘
select * from 表 where name like ‘_liu%‘

select * from 表 limit 5;            - 前5行
select * from 表 limit 4,5;          - 从第4行开始的5行
select * from 表 limit 5 offset 4    - 从第4行开始的5行

select * from 表 order by 列 asc              - 根据 “列” 从小到大排列
select * from 表 order by 列 desc             - 根据 “列” 从大到小排列
select * from 表 order by 列1 desc,列2 asc    - 根据 “列1” 从大到小排列，如果相同则按列2从小到大排序

select num from 表 group by num
select num,nid from 表 group by num,nid
select num,nid from 表  where nid > 10 group by num,nid order by nid desc
select num,nid,count(*),sum(score),max(score),min(score) from 表 group by num,nid
select num from 表 group by num having max(id) > 10
 
特别的：group by 必须在where之后，order by之前

组合，自动处理重合（去掉相同）
    select nickname from A union select name from B
 
组合，不处理重合（所有的都显示）
    select nickname from A union all select name from B

无对应关系则不显示
    select A.num, A.name, B.name from A,B Where A.nid = B.nid
 
无对应关系则不显示
    select A.num, A.name, B.name from A inner join B
    on A.nid = B.nid
 
A表所有显示，如果B中无对应关系，则值为null
    select A.num, A.name, B.name from A left join B on A.nid = B.nid
 
B表所有显示，如果B中无对应关系，则值为null
    select A.num, A.name, B.name from A right join B on A.nid=B.nid