CREATE DEFINER = CURRENT_USER PROCEDURE `NewProc`(in _xnb varchar(50))

BEGIN

    ## 定义变量

    DECLARE _num FLOAT(14,6) DEFAULT 0;

    ## @表示全局变量 相当于php $

    ## 拼接赋值 INTO 必须要用全局变量不然语句会报错

    SET @strsql = CONCAT('SELECT SUM(',_xnb,') INTO @tnum FROM btc_user_coin');

    ## 预处理需要执行的动态SQL，其中stmt是一个变量

    PREPARE stmt FROM @strsql;

    ## 执行SQL语句

    EXECUTE stmt;

    ## 释放掉预处理段

    deallocate prepare stmt;

    ## 赋值给定义的变量

    SET _num = @tnum;

    SELECT _num

END;;

SELECT SUM(fee) INTO _trade_fee_buy FROM btc_myzr WHERE `coinname`=_xnb AND addtime BETWEEN _beg AND _bend;