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WHERE約束

where字句中可以使用：

1. 1. 比較運算符：>< >= ?<= ?!=
   2. between 80 and 100 值在80到100之間 ? >=80 ?<=100
   3. in(80,90,100) 值是80或90或100 ? ?滿足這個條件就可以
   4. like 'egon%'
      pattern可以是%或_，
      %表示任意多字符
      _表示一個字符
   5. 邏輯運算符：在多個條件直接可以使用邏輯運算符 and or not

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select id,name,age?from employee where id >7;

執行順序 1.from employee ?2. where id >7 3. id,name,age

先找到表 再按照約束條件 從表里取要找的記錄

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單個條件

mysql> select id,name,age from employee where id >7;
+----+-----------+-----+
| id | name      | age |
+----+-----------+-----+
|  8 | 丫丫      |  38 |
|  9 | 丁丁      |  18 |
| 10 | 星星      |  18 |
| 11 | 格格      |  28 |
| 12 | 張野      |  28 |
| 13 | 程咬金    |  18 |
| 14 | 程咬銀    |  18 |
| 15 | 程咬銅    |  18 |
| 16 | 程咬鐵    |  18 |
+----+-----------+-----+
9 rows in set (0.11 sec)

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找出薪資大于8000的老師

多個條件

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mysql> select name,post,salary from employee where post='teacher' and salary>8000;
+------------+---------+------------+
| name       | post    | salary     |
+------------+---------+------------+
| alex       | teacher | 1000000.31 |
| jingliyang | teacher |    9000.00 |
| jinxin     | teacher |   30000.00 |
| 成龍       | teacher |   10000.00 |
+------------+---------+------------+
4 rows in set (0.00 sec)

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薪資大于等于20000 小于等于30000

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mysql> select name,salary from employee where  salary >= 20000 and salary <= 30000;
+-----------+----------+
| name      | salary   |
+-----------+----------+
| jinxin    | 30000.00 |
| 程咬金    | 20000.00 |
+-----------+----------+
2 rows in set (0.00 sec)

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between 20000 and 30000

原理 >= 20000 ?<=30000

mysql> select name,salary from employee where salary between 20000 and 30000;
+-----------+----------+
| name      | salary   |
+-----------+----------+
| jinxin    | 30000.00 |
| 程咬金    | 20000.00 |
+-----------+----------+
2 rows in set (0.00 sec)

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小于20000 或者大于30000

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mysql> select name,salary from employee where salary < 20000 or salary >30000;
+------------+------------+
| name       | salary     |
+------------+------------+
| alex       | 1000000.31 |
| yuanhao    |    3500.00 |
| liwenzhou  |    2100.00 |
| jingliyang |    9000.00 |
| 成龍       |   10000.00 |
| 歪歪       |    3000.13 |
| 丫丫       |    2000.35 |
| 丁丁       |    1000.37 |
| 星星       |    3000.29 |
| 格格       |    4000.33 |
| 張野       |   10000.13 |
| 程咬銀     |   19000.00 |
| 程咬銅     |   18000.00 |
| 程咬鐵     |   17000.00 |
+------------+------------+
14 rows in set (0.00 sec)

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between 取反

小于2000 ? 大于30000

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mysql> select name,salary from employee where salary not between 20000 and 30000;
+------------+------------+
| name       | salary     |
+------------+------------+
| alex       | 1000000.31 |
| yuanhao    |    3500.00 |
| liwenzhou  |    2100.00 |
| jingliyang |    9000.00 |
| 成龍       |   10000.00 |
| 歪歪       |    3000.13 |
| 丫丫       |    2000.35 |
| 丁丁       |    1000.37 |
| 星星       |    3000.29 |
| 格格       |    4000.33 |
| 張野       |   10000.13 |
| 程咬銀     |   19000.00 |
| 程咬銅     |   18000.00 |
| 程咬鐵     |   17000.00 |
+------------+------------+
14 rows in set (0.00 sec)

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#1:單條件查詢SELECT name FROM employeeWHERE post='sale';#2:多條件查詢SELECT name,salary FROM employeeWHERE post='teacher' AND salary>10000;#3:關鍵字BETWEEN ANDSELECT name,salary FROM employee WHERE salary BETWEEN 10000 AND 20000;SELECT name,salary FROM employee WHERE salary NOT BETWEEN 10000 AND 20000;

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轉載于:https://www.cnblogs.com/mingerlcm/p/9871636.html

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