mybatis resultType=java.util.Map 时注意返回null

利用mybatis 动态查询一条记录，而返回是一个map（resultType=”java.util.Map”，键是字段名，值是字段值），比如操作数据库是通过存储过程或者是直接传一个String sql="select * from emp where e_id=1"字符串来返回一个map。

1、如果某一列的值为空。查询这条记录时就不显示这列了。《===map中无此对应的键

2、如果这个列是number类型，不能给默认值（比如 ‘0’）。只能为空，这样也会显示不出来《===map中无此对应的键

解决办法：可以利用Oracle的nvl（）函数，比如nvl（字段，’0’）表示如果字段为空，则用0字符替代

<select id="queryLogonData" parameterType="java.util.Map" resultType="java.util.Map">
    select nvl(aa.DEVICE_CNT,0) DEVICE_CNT, nvl(aa.EVENT_CNT,0) EVENT_CNT, nvl(aa.USER_CNT,0) USER_CNT,
    bb.CAL_NUMBER from
    (select 0 as DEVICE_CNT,sum(a.event_cnt) as EVENT_CNT,count(distinct(a.user_identifier)) as
    USER_CNT,a.CAL_NUMBER
    from razor_dw_user_logon_log_day a
    where 1 = 1
<if test="version != 'all' and '' != version">
        <![CDATA[
            AND VERSION =#{version}
            ]]>
</if>
    AND a.APP_KEY IN (SELECT PRODUCTKEY FROM RAZOR_CHANNEL_PRODUCT WHERE PRODUCT_ID = #{productId})
    AND a.cal_number between #{startTime} and #{endTime}
    group by a.cal_number
    order by a.cal_number ASC) aa
    right join dim_calendar bb
    on aa.cal_number = bb.cal_number
    where bb.cal_number between #{startTime} and #{endTime}
    order by bb.cal_number ASC
</select>