在同一个 MySQL SELECT 语句中使用别名的值
mysqlmysqli database
您不能在 SELECT 中直接使用别名。相反，请使用用户定义的变量。以下是语法。这里，@yourAliasName 是我们的变量和别名−
select @yourAliasName :=curdate() as anyAliasName,concat(‘yourValue.',yourColumnName,' yourValue',@yourAliasName) as anyAliasName from yourTableName;
首先我们创建一个表 −
mysql> create table DemoTable ( Name varchar(40) ); Query OK, 0 rows affected (0.62 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values('John Smith');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('Chris Brown');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('David Miller');
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable values('John Doe');
Query OK, 1 row affected (0.18 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+--------------+ | Name | +--------------+ | John Smith | | Chris Brown | | David Miller | | John Doe | +--------------+ 4 rows in set (0.00 sec)
以下是在同一 SQL 语句中使用别名值的查询 −
mysql> select @todayDate :=curdate() as todayDate,concat('Mr.',Name,' The current Date is=',@todayDate) as Result from DemoTable;
这将产生以下输出 −
+------------+------------------------------------------------+ | todayDate | Result | +------------+------------------------------------------------+ | 2019-09-08 | Mr.John Smith The current Date is=2019-09-08 | | 2019-09-08 | Mr.Chris Brown The current Date is=2019-09-08 | | 2019-09-08 | Mr.David Miller The current Date is=2019-09-08 | | 2019-09-08 | Mr.John Doe The current Date is=2019-09-08 | +------------+------------------------------------------------+ 4 rows in set (0.00 sec)
