我可以声明在mysql命令行

Question

可以说我想要做$table = 'datatables_demo';这样的话我可以做select * from $table变量？我怎样才能做到这一点？

LOG低于

mysql> select * from datatables_demo;           +----+------------+-----------+-------------+--------+------------+--------+ 
| id | first_name | last_name | position | office | start_date | salary | 
+----+------------+-----------+-------------+--------+------------+--------+ 
| 1 | Tiger  | Nixon  | Accountant | Tokyo | 2016-11-08 | 320800 | 
| 2 | Garrett | Winters | Accountant2 | Tokyo | 2016-11-08 | 170750 | 
| 3 | Ashton  | Cox  | Accountant3 | Tokyo | 2016-11-08 | 86000 | 
| 4 | Cedric  | Kelly  | Accountant4 | Tokyo | 2016-11-08 | 433060 | 
| 5 | Tiger5  | Nixon  | Accountant | Tokyo | 2016-11-08 | 320800 | 
+----+------------+-----------+-------------+--------+------------+--------+ 
5 rows in set (0.00 sec) 

mysql> $table = 'datatables_demo'; 
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '$table = 'datatables_demo'' at line 1 
mysql> table = 'datatables_demo'; 
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'table = 'datatables_demo'' at line 1 
mysql> var table varchar2(20) 
    -> ; 

Answer 1

你应该使用PREPARE STATEMENT实现动态SQL语句。

告诉你一个例子

delimiter // 
CREATE PROCEDURE dynamic(IN tbl CHAR(64), IN col CHAR(64)) 
BEGIN 
    SET @s = CONCAT('SELECT ',col,' FROM ',tbl); 
    PREPARE stmt FROM @s; 
    EXECUTE stmt; 
    DEALLOCATE PREPARE stmt; 
END 
// 
delimiter ;