查询操作

1、别名查询

select id 序号,name名字from test_1209ryc;

2、条件查询(between)

select * from test_1209ryc where id between 2 and 5;

3、条件查询(in)

select * from test_1209ryc where id in(1,2,3);

4、子查询

select * from test_1209ryc where id in (select id from test_1209ryc where id>=5);

5、与或非的查询

select id from test_1209ryc where id >=4 and id <= 6;

select * from test_1209ryc where id>=5 and name = "qian";

select * from test_1209ryc where id>=5 or name = "qian;

select * from test_1209ryc where name="zhang" or name = "qian;

6、排序查询

select * from test_1209ryc order by id desc;

默认升序的

select * from test_1209ryc order by id;

select * from test_1209ryc order by id asc;

7、多列排序查询

(前面字段一样的时候，后面的字段在进行排序)

select * from test_1209ryc order by id,age asc;

8、仅返回一条数据

select * from test_1209ryc order by id,age asc limit 1;

9、limit 5,1(跳过5行，显示1行)

select * from test_1209ryc order by id,age asc limit 5,1;

(跳过5行，显示1行)

10、去重distinct

select distinct name 名字 from test_1209ryc;

11、统计总数(count)

select count(name) 名字from test_1209ryc;

12、统计平均值(avg)

select  avg(age) 年龄 from test_1209ryc;

13、查看当前时间戳select now()

select now()

查看当前时间(服务器的时间)

select now();

14、查看当前时间select curtime()

select curtime();

15、分组查询

select count(*),age from test_1209ryc group by age;

分组里面的条件只能用having,使用Where会报错