mybatis使用group by分组

group by

单表

sql返回多个列的 都是用 List<Map<String, Long>>，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