在 MySQL 中添加新列并根据条件在其中设置值?
mysqlmysqli database更新于 2025/5/17 11:56:17
要根据条件设置值，请使用 IF() 方法。让我们首先创建一个表 −
mysql> create table DemoTable -> ( -> Age int -> ); Query OK, 0 rows affected (0.55 sec)
使用 insert 插入命令在表中插入一些记录 −
mysql> insert into DemoTable values(19); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values(16); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(17); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(22); Query OK, 1 row affected (0.19 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
Ouptut
这将产生以下输出 −
+------+ | Age | +------+ | 19 | | 16 | | 17 | | 22 | +------+ 4 rows in set (0.00 sec)
以下是根据条件设置值的查询 −
mysql> select Age,if(Age > 18,'You are qualified!','Sorry, you are rejected!') AS Result from DemoTable;
输出
这将产生以下输出 −
+------+-------------------------+ | Age | Result | +------+-------------------------+ | 19 | You are qualified! | | 16 | Sorry, you are rejected!| | 17 | Sorry, you are rejected!| | 22 | You are qualified! | +------+-------------------------+ 4 rows in set (0.00 sec)
相关文章
有用资源
mysql 参考教程 - 该教程包含有关 mysql 的更多信息:https://www.cainiaomax.com/mysql/
