mysql时间字符串按年/月/天/时分组查询 -- date_format

SELECT DATE_FORMAT( deteline, "%Y-%m-%d %H" ) , COUNT( * )

FROM test

GROUP BY DATE_FORMAT( deteline, "%Y-%m-%d %H" )

查询某天：

deteline, "%Y-%m-%d"

某时：

deteline, "%Y-%m-%d %H"

依次类推。

其实就是对dateline进行处理，然后再对处理后的数据分组

ex:统计每小时创建的个数

 SELECT DATE_FORMAT( create_time, "%Y-%m-%d %H" ) as time , COUNT( * ) as count FROM pdca GROUP BY DATE_FORMAT( create_time, "%Y-%m-%d %H" )

Ex2:比较时间

     <select id="queryByStatusAndTime" parameterType="map" resultMap="BaseResultMap">
         select
         <include refid="Base_Column_List"/>
         from pdca
         <where>

             begin_time is not null and end_time is not null

             <if test="userId != null and userId != '' ">
                 and user_id=#{userId}
             </if>

             <if test="status != null">
                 and status in
                 <foreach collection="status" item="s" open="(" separator="," close=")">
                     #{s}
                 </foreach>
             </if>

             <if test="finishedTime != null and finishedTime != ''">
                 and date_format(finished_time, '%Y-%m')=date_format(#{finishedTime}, '%Y-%m')
             </if>

             <if test="endTime != null and endtime != ''">
                 and date_format(end_time, '%Y-%m-%d')=date_format(#{endTime}, '%Y-%m-%d')
             </if>

             <if test="endTimeLt != null and endtimeLt != ''">
                 and end_time &lt; #{endTimeLt}
             </if>

             <if test="endTimeGt != null and endtimeGt != ''">
                 and end_time &gt; #{endTimeGt}
             </if>

             <if test="beginTime != null and beginTime != ''">
                 and date_format(begin_time, '%Y-%m-%d')=date_format(#{beginTime}, '%Y-%m-%d')
             </if>

             <if test="completion != null">
                 and completion=#{completion}
             </if>
         </where>
     </select>