MairDB 查詢表(五)

     

第一部分 過濾數據 WHERE

2.1 WHERE 支持條件判斷

1. 大於: >; 2. 小於: <; 3. 等於: =; 4. 大於等於: >=; 5. 小於等於: <=; 6. 不等於: !=;

實例: 檢測單個值, 能夠將WHERE支持的條件判斷語句替換;

> SELECT * FROM books WHERE book_id = 1;

2.2 範圍檢測BETWEEN AND

> SELECT book_id, book_name FROM books WHERE book_id BETWEEN 3 AND 10; +---------+------------------+ | book_id | book_name        | +---------+------------------+ |       3 | HTTP權威指南     | |       4 | 追風箏的人       | |       5 | 小王子           | |       6 | 圍城             | |       7 | 活着             | |       8 | 解憂雜貨店       | |       9 | 簡愛             | |      10 | 平凡的世界       | +---------+------------------+

2.3 空值檢測 NULL: 列 IS NULL;

> SELECT book_id, book_name FROM books WHERE description IS NULL;

2.4 篩選 AND 先後共同知足條件

+---------+------------------+------------------+------------------+-------------+----------+------+ | book_id | book_name        | book_author_name | publication_date | description | classify | c    | +---------+------------------+------------------+------------------+-------------+----------+------+       16 | 國富論           | NULL             | 2005-01-01       | NULL        | 6        | NULL | |      17 | 偉大的博弈       | 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 | 國富論    | +---------+-----------+ 1 row in set (0.01 sec)

2.5 篩選 OR 先後 知足一個條件便可

> 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 | 國富論          | |      17 | 偉大的博弈      | +---------+-----------------+ 3 rows in set (0.00 sec)