mysql必知必会(四、检索数据，五、排序检索数据，六、过滤数据，七、数据过滤)

四、select语句

1、检索单个列

select prod_name from products;

2、检索多个列

select prod_name, prod_price from products;

3、检索所有列

select * from products;

4、检索不同的行

select distinct vend_id from products;（vend_id只返回不同的值）

5、限制结果

select prod_name from products limit 开始位置，检索行数;

6、使用完全限定的表名

select products.prod_name from products;

select products.prod_name from crashcourse.products;

五、排序检索数据

1、根据prod_name排序

select prod_name from products order by prod_name;

2、按多个列排序

select prod_id, prod_price, prod_name from products order by prod_price, prod_name;

3、指定排序方向

select prod_id, prod_price, prod_name from products order by prod_price desc;(desc降序，asc升序)

select prod_id, prod_price, prod_name from products order by price_price desc, prod_name;

select prod_price from products order by prod_price desc limit 1;

六、过滤数据

1、使用where子句

select prod_name, prod_price from products where prod_price=2.50;

where支持

=，<>,!=,<,<=,>,>=,between

2、检查单个值

select prod_name, prod_price from products where prod_name = 'fuses';

3、范围检查

select prod_name, prod_price from products where prod_price between 5 and 10;

4、空值检查

select  prod_name from products where prod_price is null;

七、数据过滤

1、and操作符

select prod_id, prod_price, prod_name from products where vend_id = 1003 and prod_price <= 10;

2、or操作符

select prod_name, prod_price from product where vend_id = 1002 or vend_id = 1003;

3、计算次序

select prod_name, prod_price from products where vend_id = 1002 or vend_id = 1003 and prod_price >= 10;（先and在or）

select prod_name, prod_price from products where （vend_id = 1002 or vend_id = 1003 ）and prod_price >= 10

4、in操作符

select prod_name, prod_price from products where vend_id in (1002, 1003) order by prod_name;

5、not操作符

select prod_name, prod_price from products where vend_id not in (1002, 1003) order by prod_name;