MairDB 查询表(五)

     

第一部分 过滤数据 WHERE

2.1 WHERE 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, 能够将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 先后共同知足条件

+---------+------------------+------------------+------------------+-------------+----------+------+ | 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 先后 知足一个条件便可

> 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)