根据参数写动态sql

不止mysql不能识别，oracle、db2一样都不能识别，印象里只有foxbase可以通过转义识别。

而在mysql、oracle、db2里就需要用动态sql

实现过程如下

DELIMITER $$
drop PROCEDURE `exe_select`$$

CREATE PROCEDURE `exe_select`(in tbl varchar(500),in col varchar(500))
begin
    set @str = concat('select ', col, ' from ', tbl);
    PREPARE stmt FROM @str;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END$$

DELIMITER ;

mysql> call exe_select('emp','empno');
+-------+
| empno |
+-------+
|  7369 |
|  7499 |
|  7521 |
|  7566 |
|  7654 |
|  7698 |
|  7782 |
|  7788 |
|  7839 |
|  7844 |
|  7876 |
|  7900 |
|  7902 |
|  7934 |
+-------+
14 rows in set (0.01 sec)

Query OK, 0 rows affected (0.01 sec)

mysql> call exe_select('emp','empno,ename');
+-------+--------+
| empno | ename  |
+-------+--------+
|  7369 | SMITH  |
|  7499 | ALLEN  |
|  7521 | WARD   |
|  7566 | JONES  |
|  7654 | MARTIN |
|  7698 | BLAKE  |
|  7782 | CLARK  |
|  7788 | SCOTT  |
|  7839 | KING   |
|  7844 | TURNER |
|  7876 | ADAMS  |
|  7900 | JAMES  |
|  7902 | FORD   |
|  7934 | MILLER |
+-------+--------+
14 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)