mysql - 在 Mysql 的存储过程中使用不同的数据库

Question

以下是我的存储过程

   DELIMITER $$

USE `us_db`$$

DROP PROCEDURE IF EXISTS `getTransactionDetails`$$

CREATE DEFINER=`root`@`localhost` PROCEDURE `getTransactionDetails`(IN _MainDB VARCHAR(32),
                                IN _mobile VARCHAR(50), 
                                IN _market_id VARCHAR(50), 
                                IN _from DATE, 
                                IN _to DATE)
BEGIN

   SELECT 
    transaction_id AS txn_id,
    DATE_FORMAT(createdon,"%d-%b-%Y %H:%i:%S") AS createdon,
    order_id,
    order_conv_total AS amount,
    msisdn AS msisdn,
    channel_id,
    transmode_id,
    statusid,
    (SELECT fullname FROM _MainDB.entities WHERE entity_id=retailer_id) AS retailer,

    FROM `us_transaction` `t` WHERE

   t.market_id = _market_id AND msisdn = _mobile AND t.createdon BETWEEN CONCAT(DATE(_from)," 00:00:00") AND CONCAT(DATE(_to)," 23:59:59") ORDER BY t.createdon DESC LIMIT 100;

    END$$

DELIMITER ;

现在的问题是零售商名称存储在一个单独的数据库中，我想通过 _MainDB 调用它。该数据库名称作为参数出现，但由于 _MainDB 被视为 varchar 类型，因此无法正确出现。如何将数据库名称作为存储过程中的参数？？？

Answer 1

用户变量和 CONCAT 函数；

DECLARE STR VARCHAR(1000)   
SET @STR = 'SELECT 
            transaction_id AS txn_id,
            ........
                            (SELECT fullname FROM  
        '
SET @STR = CONCAT(@STR,@_MAINDB)
SET @STR = CONCAT(@STR,'.entities ..................')      

PREPARE STMT FROM @STR
EXECUTE STMT