数据库教程-mariadb教程-MariaDB Where子句

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在MariaDB中,WHERE子句与SELECTINSERTUPDATEDELETE语句一起使用来选择或更改想要更改的满足指定特定行记录。

它是一个在表名后面出现的语句。

语法

[COMMAND] field,field2,... FROM table_name,table_name2,... WHERE [CONDITION] 

1. WHERE子句与单一条件

示例:

我们有一个表students,里边有一些数据。假设要查询students表中的student_id小于6的所有记录。

SELECT *    FROM Students   WHERE student_id < 6; 

执行上面查询语句,得到以下结果 –

MariaDB [testdb]> SELECT *     -> FROM Students     -> WHERE student_id < 6; +------------+--------------+-----------------+----------------+ | student_id | student_name | student_address | admission_date | +------------+--------------+-----------------+----------------+ |          1 | Maxsu        | Haikou          | 2017-01-07     | |          3 | JMaster      | Beijing         | 2016-05-07     | |          4 | Mahesh       | Guangzhou       | 2016-06-07     | |          5 | Kobe         | Shanghai        | 2016-02-07     | +------------+--------------+-----------------+----------------+ 4 rows in set (0.00 sec) 

2. WHERE子句与AND条件

为了方便演示,这里再插入一条数据 –

INSERT INTO students   (student_name, student_address, admission_date)   VALUES('Maxsu','Sanya','2017-08-08 00:00:00'); 

当前students表中的全部数据是 –

MariaDB [testdb]> select * from students; +------------+--------------+-----------------+----------------+ | student_id | student_name | student_address | admission_date | +------------+--------------+-----------------+----------------+ |          1 | Maxsu        | Haikou          | 2017-01-07     | |          3 | JMaster      | Beijing         | 2016-05-07     | |          4 | Mahesh       | Guangzhou       | 2016-06-07     | |          5 | Kobe         | Shanghai        | 2016-02-07     | |          6 | Blaba        | Shengzhen       | 2016-08-07     | |          7 | Maxsu        | Sanya           | 2017-08-08     | +------------+--------------+-----------------+----------------+ 6 rows in set (0.00 sec) 

现在要查询students表中的所有列,其中student_nameMaxsu,并且student_id大于1的行记录。这两个条件都必须满足。参考以下查询语句 –

SELECT *   FROM Students   WHERE student_name = 'Maxsu'   AND student_id >1 ; 

执行上面查询语句,得到以下结果 –

MariaDB [testdb]> SELECT *     -> FROM Students     -> WHERE student_name = 'Maxsu'     -> AND student_id >1 ; +------------+--------------+-----------------+----------------+ | student_id | student_name | student_address | admission_date | +------------+--------------+-----------------+----------------+ |          7 | Maxsu        | Sanya           | 2017-08-08     | +------------+--------------+-----------------+----------------+ 1 row in set (0.03 sec) 

3. WHERE子句与OR条件

现在要查询students表中的所有列,其中student_nameMaxsu,或者student_id大于5的行记录。这两个条件满足其中一个即可。参考以下查询语句 –

SELECT *   FROM Students   WHERE student_name = 'Maxsu' OR student_id >5 ; 

执行上面查询语句,得到以下结果 –

MariaDB [testdb]> SELECT *     -> FROM Students     -> WHERE student_name = 'Maxsu'     -> OR student_id >5 ; +------------+--------------+-----------------+----------------+ | student_id | student_name | student_address | admission_date | +------------+--------------+-----------------+----------------+ |          1 | Maxsu        | Haikou          | 2017-01-07     | |          6 | Blaba        | Shengzhen       | 2016-08-07     | |          7 | Maxsu        | Sanya           | 2017-08-08     | +------------+--------------+-----------------+----------------+ 3 rows in set (0.00 sec) 

4. WHERE子句与OR/AND条件

假设要查询students表中的所有列,那些符合student_nameAjeetstudent_id大于或等于1,或者student_addressShanghai的行记录。

SELECT *   FROM Students   WHERE student_name = 'Maxsu'    AND student_id >=1 OR (student_address = 'Shanghai'); 

执行上面查询语句,得到以下结果 –

MariaDB [testdb]> SELECT *     -> FROM Students     -> WHERE student_name = 'Maxsu'     -> AND student_id >=1     -> OR (student_address = 'Shanghai'); +------------+--------------+-----------------+----------------+ | student_id | student_name | student_address | admission_date | +------------+--------------+-----------------+----------------+ |          1 | Maxsu        | Haikou          | 2017-01-07     | |          5 | Kobe         | Shanghai        | 2016-02-07     | |          7 | Maxsu        | Sanya           | 2017-08-08     | +------------+--------------+-----------------+----------------+ 3 rows in set (0.00 sec) 

  

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