常用写法
xxxDO=实体类， 相当于:
select name, id from xxx group by name where delete_flag = 0 and status = 0
LambdaQueryWrapper<xxxDO> queryWrapper = Wrappers.lambdaQuery();
queryWrapper.select(xxxDO::getName, DO::getId);
queryWrapper.eq(xxxDO::getDeleteFlag, 0);
queryWrapper.eq(xxxDO::getStatus, 0);
queryWrapper.groupBy(xxxDO::getName);
List<xxxDO> list = getBaseMapper().selectList(queryWrapper);自定义sql
xxxDO=实体类，相当于:
select sex, ifnull(count(id), 0) AS num, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' ELSE '未知' END AS sexStr from xxx group by sex where status = 0
LambdaQueryWrapper<xxxDO> queryWrapper = new QueryWrapper<xxxDO>()
.select("sex, ifnull(count(id), 0) AS num, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' ELSE '未知' END AS sexStr").lambda();
queryWrapper.eq(xxxDO::getStatus, 0);
queryWrapper.groupBy(xxxDO::getSex);
List<Map<String, Object>> mapList = getBaseMapper().selectMaps(queryWrapper);
Map<String, String> registerNumMap = new HashMap<>(mapList.size());
for (Map<String, Object> map : mapList) {
String key = String.valueOf(map.get("sexStr"));
String num = String.valueOf(map.get("num"));
registerNumMap.put(key, num);
}返回结果是一个list, 里面的map key是查询的属性名， value是参数值。伪代码示意：
list[0]
map[0] (sex=1)
map[1] (num=5)
map[2] (sexStr=男)
list[1]
map[0] (sex=1)
map[1] (num=5)
map[2] (sexStr=男)
偶然而发， 记录一下
补充: 查询条件中使用函数apply
queryWrapper.apply("INET_ATON(qsip) <= INET_ATON({0})", ipQuery);
queryWrapper.apply("INET_ATON(zzip) >= INET_ATON({0})", ipQuery);补充: 末尾sql追加last
queryWrapper.last(" order by id asc");
queryWrapper.last("limit 1");补充:排序
// last也可以追加limit 这里用page接口
IPage<Entity> buildPage = new Page<>(0, 200);
// ServiceImpl的page调用的是baseMapper的selectPage, getBaseMapper().selectPage()
IPage<Entity> page = page(buildPage, queryWrapper);sql打印
补充：Mybatis-Plus QueryWrapper sql自定义查询
一： 需要自定义的QueryWrapper查询工具类，定义查询规则
public static final String SQL_RULES_COLUMN = "SQL_RULES_COLUMN"; private static final String BEGIN = "_begin"; // 字段范围查询开始标识 private static final String END = "_end"; // 字段范围查询结束标识 private static final String STAR = "*"; // 字段模糊查询标识 private static final String COMMA = ","; private static final String NOT_EQUAL = "!";
二： 正常的QueryWrapper查询，在mapper文件中使用 @Param(Constants.WRAPPER)
List<Emdj> listAll(IPage<Emdj> page, @Param(Constants.WRAPPER) QueryWrapper<Emdj> queryWrapper);
xml文件中使用ew.customSqlSegment，<where>标签可以不加
<select id="listAll" resultType="net.zazn.modules.discipline.entity.Emdj">
select id,lffh,xm,jsh,szrq,emlx,spzt,gjmj,flag,jlzt
from emdj
<where>${ew.customSqlSegment}</where>
</select>
总结
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