第一部分过滤数据WHERE
2.1WHERE支持条件判断
1. 大于: >;
2. 小于: <;
3. 等于: =;
4. 大于等于: >=;
5. 小于等于: <=;
6. 不等于: !=;
实例: 检测单个值, 可以将WHERE支持的条件判断语句替换;
> SELECT * FROM books WHERE book_id = 1;
2.2 范围检测BETWEEN AND
> SELECT book_id, book_name FROM books WHERE book_id BETWEEN 3 AND 10;
+---------+------------------+
| book_id | book_name |
+---------+------------------+
| 3 | HTTP权威指南 |
| 4 | 追风筝的人 |
| 5 | 小王子 |
| 6 | 围城 |
| 7 | 活着 |
| 8 | 解忧杂货店 |
| 9 | 简爱 |
| 10 | 平凡的世界 |
+---------+------------------+
2.3空值检测NULL:列IS NULL;
> SELECT book_id, book_name FROM books WHERE description IS NULL;
2.4筛选AND前后共同满足条件
+---------+------------------+------------------+------------------+-------------+----------+------+
| book_id | book_name | book_author_name | publication_date | description | classify | c |
+---------+------------------+------------------+------------------+-------------+----------+------+
16 | 国富论 | NULL | 2005-01-01 | NULL | 6 | NULL |
| 17 | 伟大的博弈 | NULL | 2005-01-01 | NULL | 6 | NULL |
> SELECT book_id, book_name FROM books WHERE book_id = 16 AND publication_date = '2005-01-01';
+---------+-----------+
| book_id | book_name |
+---------+-----------+
| 16 | 国富论 |
+---------+-----------+
1 row in set (0.01 sec)
2.5筛选OR前后 满足一个条件即可
> SELECT book_id, book_name FROM books WHERE book_id = 16 OR publication_date = '2005-01-01';
+---------+-----------------+
| book_id | book_name |
+---------+-----------------+
| 10 | 平凡的世界 |
| 16 | 国富论 |
| 17 | 伟大的博弈 |
+---------+-----------------+
3 rows in set (0.00 sec)
