表格:
选择查询:
select 字段 from 表名;
select id,name from students;
消除重复行:
select distinct 字段 from students;
select distinct gender from student;
查询 where的使用:
where是筛选行,select是筛选列
select 字段 from 表 where 条件;
select gender from students where gender = 0 ;
having和where 有时候可以互换,例如:
select gender from students having gender = 1;
但是,如果同时用where和having,having需要排在where后面,having是对筛选出的结果集再进行筛选,例如:
select name from students where gender = 1 having name='xiaohua';