mysql数据库—表的查询排序操作大全

表的查询操作

　　select * from 表  *效率低
　　select * from 表 where id > 1
　　select nid,name,gender as gg from 表 where id > 1　　　　as相当于取别名，别名为gg
　　select count(id) from userinfo5;  查询表内有多少条数据

　　select * from tb12;   
   select id,name from tb12;   
   select id,name from tb12 where id > 10 or name ='xxx';   
   select id,name as cname from tb12 where id > 10 or name ='xxx';   
   select name,age,11 from tb12;   多加了一列11

  其他：
    select * from tb12 where id != 1
    select * from tb12 where id in (1,5,12);  
    select * from tb12 where id not in (1,5,12);
    select * from tb12 where id in (select id from tb11)
    select * from tb12 where id between 5 and 12;   闭区间

通配符：    
    select * from tb12 where name like "a%"   以a开头的所有（多个字符）
    select * from tb12 where name like "a_"   以a开头的所有（一个字符）
分页：    
     select * from tb12 limit 10;     
     select * from tb12 limit 0,10;    0开始位置行，10查看的行数
     select * from tb12 limit 10,10;
     select * from tb12 limit 20,10;     
     select * from tb12 limit 10 offset 20;  20开始位置行，10查看的行数
排序：
     select * from tb12 order by id desc; 大到小
     select * from tb12 order by id asc;  小到大
     select * from tb12 order by age desc,id desc;   按优先级安序排列
      
     取后10条数据
     select * from tb12 order by id desc limit 10;
分组：
    
     select count(id),part_id from userinfo5 group by part_id;   统计数量
     select max(id),part_id from userinfo5 group by part_id;  part_id重合时，id取max
     select nin(id),part_id from userinfo5 group by part_id;
     
     聚合函数（去除重复）
     count
     max
     min
     sum
     avg 平均值
     
     **** 如果对于聚合函数结果进行二次筛选时？必须使用having ****
     select count(id),part_id from userinfo5 group by part_id having count(id) > 1;     
     select count(id),part_id from userinfo5 where id > 0 group by part_id having count(id) > 1;

连表操作：                    
select * from userinfo5,department5 where userinfo5.part_id = department5.id     
select * from userinfo5 left join department5 on userinfo5.part_id = department5.id      
# 左连接：userinfo5右边允许有空                 
select * from userinfo5 right join department5 on userinfo5.part_id = department5.id      
# 右连接：department5左边允许有空               
select * from userinfo5 inner join department5 on userinfo5.part_id = department5.id      
# 内连接：不会出现null
select * from userinfo5 full join department5 on userinfo5.part_id = department5.id
# 完全连接：左右都可能出现null 
 
 
g、组合（上下连表）

   组合，自动处理重合

   select nickname from A union select name from B

   组合，不处理重合
   select nickname from A union all select name from B