一、数据库的格式如下：




可以看出fix_time日期格式是：yyyy-MM-dd的格式，但是我只需要根据年月格式去查询。

首先根据fix_time时间分组，然后使用DATE_FORMAT() 函数用于以不同的格式显示日期/时间数据。
代码如下：
<select id="last12MonthsList" resultMap="BaseResultMap"  parameterType="java.util.List" >
    select
    COUNT(*),
    DATE_FORMAT(fix_time, '%Y-%m') as fix_time
    from
    cars
    where
    unit_id IN
    <foreach collection="unitIdList" item="unitIdList" open="(" separator="," close=")">
        #{unitIdList}
    </foreach>
    AND  DATE_FORMAT(fix_time, '%Y-%m') IN
    <foreach collection="list" item="list" open="(" separator="," close=")">
        #{list}
    </foreach>
    GROUP BY  DATE_FORMAT(fix_time, '%Y-%m')
</select>

select fix_time, COUNT(*) from cars where DATE_FORMAT(fix_time,'%Y-%m') = '2019-03'