在同一MySQL SELECT语句中使用别名的值
您不能在SELECT中直接使用别名。而是使用用户定义的变量。以下是语法。在这里，@yourAliasName是我们的变量和别名-
select @yourAliasName :=curdate() as anyAliasName,concat(‘yourValue.',yourColumnName,' yourValue',@yourAliasName) as anyAliasName from yourTableName;
让我们首先创建一个表-
mysql> create table DemoTable ( Name varchar(40) );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('John Smith');
mysql> insert into DemoTable values('Chris Brown');
mysql> insert into DemoTable values('David Miller');
mysql> insert into DemoTable values('John Doe');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)