1. 使用WHERE子句
SELECT
prod_name,
prod_price
FROM
products
WHERE
prod_price = 2.50;
2. WHERE子句操作符
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 |
3. 检查单个值
SELECT
prod_name,
prod_price
FROM
products
WHERE
prod_name = 'fuses';
SELECT
prod_name,
prod_price
FROM
products
WHERE
prod_price < 10;
SELECT
prod_name,
prod_price
FROM
products
WHERE
prod_price <= 10;
4. 不匹配检查
SELECT
vend_id,
prod_name
FROM
products
WHERE
vend_id <> 1003;
SELECT
vend_id,
prod_name
FROM
products
WHERE
vend_id != 1003;
5. 范围值检查
SELECT
prod_name ,
prod_price
FROM
products
WHERE
prod_price BETWEEN 5 AND 10;
6. 空值检查
SELECT
cust_id
FROM
customers
WHERE
cust_email IS NULL;
- ( NULL无值 )与 0 和 空字符串 或者空格 不同