mybatis 的 配置文件中 sql 的IFNULL问题

SELECT
            IFNULL(CAST(TRUNCATE(AVG(inflow_cod),2) AS CHAR),'') inflow_cod,
            IFNULL(CAST(TRUNCATE(AVG(inflow_nh),2) AS CHAR),'') inflow_nh,
            IFNULL(CAST(TRUNCATE(AVG(inflow_nh4),2) AS CHAR),'') inflow_nh4,
            IFNULL(CAST(TRUNCATE(AVG(inflow_p),2) AS CHAR),'') inflow_p,
            IFNULL(CAST(TRUNCATE(AVG(inflow_ph),2) AS CHAR),'') inflow_ph,
            IFNULL(CAST(TRUNCATE(AVG(inflow_ss),2) AS CHAR),'') inflow_ss,
            DATE_FORMAT(detail_date, '%Y-%m-%d') date

        FROM
            ws_sewage_monitor 
    
        GROUP BY
            DATE_FORMAT(detail_date, '%d')
        ORDER BY
            date

resultType="map"时 如果IFNULL中前后数据类型不一样会出现取值为乱码的问题  必须是ifnull 中前后数据类型一致