查詢數據(DQL)-select:
1、選擇特定的字段
select id,name from user;
2、給字段取別名-as
select id,name from user;
select id maoxian,name from user;
select id as maoxian,name from user;
3、distinct關鍵字的使用
select distinct age from user;
4、使用where條件進行查詢
select * from user where id>=3 and id<=5;
5、查詢空值
select * from user where age is null;
select * from user whrer age is not null;
6、between and的使用
select * from user where id between 3 and 5;
7、in的使用方法
select * form user where id=1 or id=2 or id=10;
select * from user where id in(1,2,10);
8、like的使用方法
_匹配一個字符
//%在前,name這一列的索引會失效
select * from user where name like "%mysql%";
9、regexp正則檢測
select * from user where username regexp 'php';
select * from user where username regexp '^php';
select * from user where username regexp 'php$';
10、使用order by對查詢結果排序
select * from user order by id asc;//默認就是升序,數字從小到大
select * from user order by id desc;//升序變爲降序,數字從大到小