MariaDB Where子句
在MariaDB中，WHERE子句與SELECT，INSERT，UPDATE和DELETE語句一起使用來選擇或更改想要更改的滿足指定特定行記錄。
它是一個在表名後面出現的語句。
語法
[COMMAND] field,field2,... FROM table_name,table_name2,... WHERE [CONDITION]注意：
WHERE子句是一個可選的子句。它可以和AND，OR，AND & OR，LIKE運算符一起使用。
1. WHERE子句與單一條件
示例：
我們有一個表students，裏邊有一些數據。假設要查詢students表中的student_id小於6的所有記錄。
SELECT *
FROM Students
WHERE student_id < 6;執行上面查詢語句，得到以下結果 -
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子句與AND條件
爲了方便演示，這裏再插入一條數據 -
INSERT INTO students
(student_name, student_address, admission_date)
VALUES('Maxsu','Sanya','2017-08-08 00:00:00');當前students表中的全部數據是 -
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)現在要查詢students表中的所有列，其中student_name是Maxsu，並且student_id大於1的行記錄。這兩個條件都必須滿足。參考以下查詢語句 -
SELECT *
FROM Students
WHERE student_name = 'Maxsu'
AND student_id >1 ;執行上面查詢語句，得到以下結果 -
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子句與OR條件
現在要查詢students表中的所有列，其中student_name是Maxsu，或者student_id大於5的行記錄。這兩個條件滿足其中一個即可。參考以下查詢語句 -
SELECT *
FROM Students
WHERE student_name = 'Maxsu'
OR student_id >5 ;執行上面查詢語句，得到以下結果 -
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子句與OR/AND條件
假設要查詢students表中的所有列，那些符合student_name是Ajeet，student_id大於或等於1，或者student_address是Shanghai的行記錄。
SELECT *
FROM Students
WHERE student_name = 'Maxsu'
AND student_id >=1
OR (student_address = 'Shanghai');執行上面查詢語句，得到以下結果 -
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)