MySQL ORDER BY 使用数字用户定义变量?
mysqlmysqli database
首先我们创建一个表 −
mysql> create table DemoTable1898 ( Number int ); Query OK, 0 rows affected (0.00 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1898 values(10); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1898 values(70); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1898 values(30); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1898 values(50); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1898 values(40); Query OK, 1 row affected (0.00 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable1898;
这将产生以下输出 −
+--------+ | Number | +--------+ | 10 | | 70 | | 30 | | 50 | | 40 | +--------+ 5 rows in set (0.00 sec)
这是使用数字用户定义变量执行 ORDER BY 的查询 −
mysql> set @limitValue:=1;
Query OK, 0 rows affected (0.00 sec)
mysql> set @query:=CONCAT('select * from DemoTable1898 order by ',@limitValue);
Query OK, 0 rows affected (0.00 sec)
mysql> prepare stmt from @query;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> execute stmt;
这将产生以下输出 −
+--------+ | Number | +--------+ | 10 | | 30 | | 40 | | 50 | | 70 | +--------+ 5 rows in set (0.00 sec)
这是解除准备查询的查询 −
mysql> deallocate prepare stmt; Query OK, 0 rows affected (0.00 sec)
