1、过滤数据
(1)使用where语句
SELECT prod_name, prod_price FROM products WHERE prod_price = 2.50;
(2)操作符
操 作 符 | 说 明 |
---|---|
= | 等于 |
<> | 不等于 |
!= | 不等于 |
< | 小于 |
<= | 小于等于 |
> | 大于 |
>= | 大于等于 |
BETWEEN | 在指定的两个值之间 |
#BETWEEN
SELECT prod_name, prod_price FROM products WHERE prod_price BETWEEN 5 AND 10;
# 检测空值
SELECT prod_name FROM products WHERE prod_price IS NULL
2、数据过滤
(1)组合WHERE 子句
# AND
SELECT prod_id, prod_price, prod_name FROM products WHERE vend_id=1003 AND prod_price<=10;
# OR
SELECT prod_name, prod_price
FROM products
WHERE cend_id=1002 OR vend_id=1003;
p.s. 多个子句时使用圆括号进行操作
(2)IN 和 NOT 操作符
# IN
SELECT prod_name, prod_price
FROM products
WHERE vend_id IN (1002,1003);
# NOT
SELECT prod_name, prod_price
FROM products
WHERE vend_id NOT IN (1002, 1003);
IN操作符一般比OR操作符清单执行更快。
IN的最大优点是可以包含其他SELECT语句,使得能够更动态地建
立WHERE子句。第14章将对此进行详细介绍。