group by

单表

sql返回多个列的 都是用 List<Map>，注意：返回的计算结果都是Long类型

@MapKey("ltStatus")List<Map<String, Object>> groupBy1();List<Map<String, Object>> groupBy2();
<select id="groupBy1" resultType="java.util.Map">    select login_name as lt_status, count(*)    from `user`    group by lt_status</select><select id="groupBy2" resultType="java.util.Map">    select login_name, count(*)    from `user`    group by login_name</select>

@MapKey是group by的字段驼峰命名

groupBy1，map有两个元素

  • lt_status为key，value是login_name的字段值
  • count(*)为key，value是计算的结果

groupBy2，map有连个元素

  • login_name为key，value是 login_name字段值
  • count(*)为key，value是计算的结果
@MapKey("userId")List<Map<String, Object>> guanlian();@MapKey("userId")List<Map<String, Object>> guanlian2();
<select id="guanlian" resultType="java.util.Map">    select o.user_id, count(1)    from `order` o, `user` u    where u.user_id = o.user_id    group by o.user_id</select><select id="guanlian2" resultType="java.util.Map">    select o.user_id , count(1) as num    from `order` o, `user` u    where u.user_id = o.user_id    group by o.user_id</select>

guanlian

  • user_id为key

guanlian2

  • 第一个元素 user_id为key
  • 第二个元素 num为key

尽量查询出来 在service层使用stream进行分组