import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.TableFieldInfo;
import com.baomidou.mybatisplus.core.metadata.TableInfo;
import com.baomidou.mybatisplus.core.metadata.TableInfoHelper;
import com.baomidou.mybatisplus.core.toolkit.Assert;
import com.baomidou.mybatisplus.core.toolkit.LambdaUtils;
import com.baomidou.mybatisplus.core.toolkit.support.LambdaMeta;
import com.baomidou.mybatisplus.core.toolkit.support.SFunction;
import org.apache.ibatis.reflection.property.PropertyNamer;

public List<Book> bookSum() {
        QueryWrapper<Book> queryWrapper = new QueryWrapper<>();
        queryWrapper.lambda()
                .gt(Book::getId, 1)
                .lt(Book::getNumOne, 10010)
                .gt(Book::getNumTow, 10000)
        ;
        addSumSql(Book.class, queryWrapper, Book::getNumOne, Book::getNumTow);
        Book sumInfo = this.bookMapper.selectOne(queryWrapper);
        return Collections.singletonList(sumInfo);
    }

    @SafeVarargs
    private final <E> void  addSumSql(Class<E> entityClass, QueryWrapper<E> queryWrapper, SFunction<E, ?>... sumFieldFns) {
        TableInfo tableInfo = TableInfoHelper.getTableInfo(entityClass);
        Assert.notNull(tableInfo, "实体的表信息不存在," + entityClass.getName());
        List<String> fieldList = new ArrayList<>();
        for (SFunction<E, ?> esFunction : sumFieldFns) {
            LambdaMeta meta = LambdaUtils.extract(esFunction);
            String fieldName = PropertyNamer.methodToProperty(meta.getImplMethodName());
            fieldList.add(fieldName);
        }
        List<TableFieldInfo> tableFieldInfoList = tableInfo.getFieldList().stream().filter(field -> fieldList.contains(field.getProperty()))
                .collect(Collectors.toList());
        Assert.notEmpty(tableFieldInfoList, "表字段信息为空," + entityClass.getName());

        String sumSelectSql = tableFieldInfoList.stream().map(tableFieldInfo -> "SUM(" + tableFieldInfo.getColumn() +") AS " + tableFieldInfo.getColumn())
                .collect(Collectors.joining(","));
        queryWrapper.select(sumSelectSql);
    }

输出的SQL如下：

[nio-8080-exec-1] c.e.demo.mapper.BookMapper.selectList : ==> Preparing: SELECT SUM(num_one) AS num_one,SUM(num_tow) AS num_tow FROM book WHERE (id > ? AND num_one < ? AND num_tow > ?)
[nio-8080-exec-1] c.e.demo.mapper.BookMapper.selectList : ==> Parameters: 1(Integer), 10010(Integer), 10000(Integer)

注：通过使用MyBatisPlus和ibatis提供的方法来获取表字段名，进行sum语句的拼接，从而达到sum函数的调用 。此方法可在3.5.0以上版本，其它版本可自行改动，故会有版本升级带来的不兼容性。