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;