是否可以在 MyBatis 中使用聚合函数

Question

I am a newbie to MyBatis. As per my knowledge every column is mapped to a property value while retrieving data from the database. So is it possible to use aggregate functions using MyBatis. To what property we will map the results? I have searched it everywhere But can't find any details about the usage of aggregate functions with MyBatis. If anyone can help, please.

Answer 1

Every column of the result set is mapped to a property. Therefore, it's just a matter of producing a SQL statement that does that.

For example:

<resultMap id="regionProfit" type="app.RegionProfitVO">
  <result property="region" column="region" />
  <result property="cnt" column="cnt" />
  <result property="profit" column="profit" />
</resultMap>

<select id="getRegionProfit" resultMap="regionProfit">
  select
    region,
    count(sales) as cnt,
    sum(revenue) - sum(expenses) as profit 
  from sales
  group by region
</select>

Now, in the Java code you could do something like:

List<RegionProfitVO> rp = sqlSession.selectList("getRegionProfit");

Answer 2

If you don't want to create another POJO, you can always retrieve the result as a list of java.util.Map<String, Object> but use resultType="hashmap" in mapper.xml file for that select query