Question

我尝试在存储过程中对另一个数据库（同一服务器）进行一次查询。一切都还可以，但我需要使用从参数中收到的动态数据库名称。

CREATE PROCEDURE my_sp(
 IN in_db_name VARCHAR(32),
 OUT out_result VARCHAR(32)
)
BEGIN   
  /*This working OK*/
  SELECT my_col INTO out_result FROM another_db.my_table WHERE id = 1;

  /*This NOT WORK :( */
  SELECT my_col INTO out_result FROM @in_db_name.my_table WHERE id = 1;
END;

Answer 1

您需要为此目的使用动态查询。

CREATE PROCEDURE my_sp(
 IN in_db_name VARCHAR(32),
 OUT out_result VARCHAR(32)
)
SET @s =  (concat ("SELECT my_col INTO out_result FROM " ,  in_db_name.my_table , " WHERE id = 1;"
    PREPARE stmt FROM @s;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END

Answer 2

尝试：

DELIMITER //

CREATE PROCEDURE `my_sp` (
    IN `in_db_name` VARCHAR(32),
    OUT `out_result` VARCHAR(32)
)
BEGIN   
    SET @`query` := CONCAT('SELECT `my_col` INTO @`_out_result` 
                            FROM `', `in_db_name`, '`.`my_table` 
                            WHERE `id` = 1');
    PREPARE `stmt` FROM @`query`;
    EXECUTE `stmt`;
    SET `out_result` := @`_out_result`;
    DEALLOCATE PREPARE `stmt`;
END//

DELIMITER ;

请参阅14.5 Prepared SQL Statement Syntax。

示例：

mysql> DROP TABLE IF EXISTS `my_table`;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE IF NOT EXISTS `my_table` (
    ->     `id` BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    ->     `my_col` VARCHAR(32) NOT NULL
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO `my_table` (`my_col`)
    -> VALUES ('ONE');
Query OK, 1 row affected (0.00 sec)

mysql> DELIMITER //

mysql> CREATE PROCEDURE `my_sp` (
    ->     IN `in_db_name` VARCHAR(32),
    ->     OUT `out_result` VARCHAR(32)
    -> )
    -> BEGIN   
    ->     SET @`query` := CONCAT('SELECT `my_col` INTO @`_out_result` 
    '>                             FROM `', `in_db_name`, '`.`my_table` 
    '>                             WHERE `id` = 1');
    ->     PREPARE `stmt` FROM @`query`;
    ->     EXECUTE `stmt`;
    ->     SET `out_result` := @`_out_result`;
    ->     DEALLOCATE PREPARE `stmt`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `my_sp`('test', @`my_out_result`);
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @`my_out_result`;
+------------------+
| @`my_out_result` |
+------------------+
| ONE              |
+------------------+
1 row in set (0.00 sec)

MySQL存储过程从参数中设置动态查询

2 个答案: