mysql必知必会（三）过滤数据（where子句指定搜索条件）

叁歲伎倆 2023-02-22 12:14 28阅读 0赞

### 文章目录 ###

*  相等测试
 *  where子句操作符
 *  总结

# 相等测试 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0_size_16_color_FFFFFF_t_70]

# where子句操作符 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0_size_16_color_FFFFFF_t_70 1]

mysql> select prod_name, prod_price
        -> from products
        -> where prod_name = 'fuses';
    Empty set (0.00 sec)

注意相等测试不是用==，就用赋值符号，这和其他语言都不一样

不匹配测试

mysql> select prod_name, prod_price
        -> from products
        -> where prod_name <> 'fuses';
    +---------------------+------------+
    | prod_name           | prod_price |
    +---------------------+------------+
    | Fish bean bag toy   |       3.49 |
    | Bird bean bag toy   |       3.49 |
    | Rabbit bean bag toy |       3.49 |
    | 8 inch teddy bear   |       5.99 |
    | 12 inch teddy bear  |       8.99 |
    | 18 inch teddy bear  |      11.99 |
    | Raggedy Ann         |       4.99 |
    | King doll           |       9.49 |
    | Queen doll          |       9.49 |
    +---------------------+------------+
    9 rows in set (0.00 sec)

范围值检查

空值检查

mysql> select prod_name, prod_price
        -> from products
        -> where prod_price is null;
    Empty set (0.00 sec)

# 总结 #

*  order by子句必须在where子句之后

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200703141202398.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200703141339663.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2NjA3ODk0,size_16,color_FFFFFF,t_70