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MySQL数据库（29）：流程结构 if while

 1 year ago
source link: https://blog.51cto.com/u_13567403/5380002
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流程结构 if while

两种基本用法

1、用在select查询中

if(条件, 结果为真, 结果为假);

mysql> select * from my_student;
+----+-----------+----------+------+--------+
| id | name      | class_id | age  | gender |
+----+-----------+----------+------+--------+
|  1 | 刘备      |        1 |   18 |      2 |
|  2 | 李四      |        1 |   19 |      1 |
|  3 | 王五      |     NULL |   20 |      2 |
|  4 | 张飞      |     NULL |   21 |      1 |
|  5 | 关羽      |     NULL |   22 |      2 |
|  6 | 曹操      |        1 |   20 |   NULL |
| 10 | 司马懿    |        6 |   26 |      1 |
+----+-----------+----------+------+--------+

mysql> select *, if(age > 20, '符合', '不符合') as result from my_student;
+----+-----------+----------+------+--------+-----------+
| id | name      | class_id | age  | gender | result    |
+----+-----------+----------+------+--------+-----------+
|  1 | 刘备      |        1 |   18 |      2 | 不符合    |
|  2 | 李四      |        1 |   19 |      1 | 不符合    |
|  3 | 王五      |     NULL |   20 |      2 | 不符合    |
|  4 | 张飞      |     NULL |   21 |      1 | 符合      |
|  5 | 关羽      |     NULL |   22 |      2 | 符合      |
|  6 | 曹操      |        1 |   20 |   NULL | 不符合    |
| 10 | 司马懿    |        6 |   26 |      1 | 符合      |
+----+-----------+----------+------+--------+-----------+
7 rows in set (0.00 sec)

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