mysql分組和排序操作

分組、排序操作      

                                                                                

 select * from student order by id desc,height asc;                                                         排序,mysql默認根據主鍵正序排列,order by 排序字段,asc正序,desc倒序,防止一個條件相同內容導致無法排序,再增加第二個排序條件進行排序       

                           

 select count(*),gender from student group by gender;                                                   group by分組,以gender分組,select與from之間為打印出來的內容,分別統計男、女人數                          

 

select count(*),age from student where age = 20 group by age;                                  打印student表格里年齡為20的人數  

                            

 select count(*),age,group_concat(id) from student where age = 20 group by age;           

                      

 select gender,count(*) from student group by gender having count(*) > 3;                  student表格里以gender分組,打印gender與count個數,having必須跟group by使用,是在分組后二次篩選                          

 

select * from student limit 1,2;                                                                                         limit限制 1:從第二個開始,取2個數據   

                             

 select * from student order by rand() limit 1,2;                                                                order by rand()隨機取數據         

                       

select gender,count(*) from student group by gender with rollup;                                       以gender分組,gender和count,   with rollup累加count