mirror of
https://gitee.com/best_handsome/mybatis-plus-join
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256 lines
8.2 KiB
Markdown
256 lines
8.2 KiB
Markdown
# mybatis-plus-join
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* 对 [mybatis-plus](https://gitee.com/baomidou/mybatis-plus) 多表查询的扩展
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* [演示工程](https://gitee.com/best_handsome/mybatis-plus-join-demo)
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* 点个Star支持一下吧 :)
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QQ群:1022221898
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## 使用方法
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### 安装
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- Maven
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```xml
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<dependency>
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<groupId>com.github.yulichang</groupId>
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<artifactId>mybatis-plus-join</artifactId>
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<version>1.3.3</version>
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</dependency>
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```
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- Gradle
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```
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implementation 'com.github.yulichang:mybatis-plus-join:1.3.3'
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```
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或者clone代码到本地执行 mvn install, 再引入以上依赖
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<br>
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注意: mybatis plus version >= 3.4.0
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<br>
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### 使用
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* mapper继承MPJBaseMapper (必选)
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* service继承MPJBaseService (可选)
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* serviceImpl继承MPJBaseServiceImpl (可选)
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### Lambda形式用法（MPJLambdaWrapper）
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#### 简单的连表查询
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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void testJoin() {
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//和Mybatis plus一致，MPJLambdaWrapper的泛型必须是主表的泛型，并且要用主表的Mapper来调用
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MPJLambdaWrapper<UserDO> wrapper = new MPJLambdaWrapper<UserDO>()
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.selectAll(UserDO.class)//查询user表全部字段
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.select(UserAddressDO::getTel)//查询user_address tel 字段
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.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)//别名 t.address AS userAddress
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.select(AreaDO::getProvince, AreaDO::getCity)
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.leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
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.leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId)
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.eq(UserDO::getId, 1)
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.like(UserAddressDO::getTel, "1")
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.gt(UserDO::getId, 5);
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//连表查询 返回自定义ResultType
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List<UserDTO> list = userMapper.selectJoinList(UserDTO.class, wrapper);
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//分页查询 （需要启用 mybatis plus 分页插件）
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List<UserDTO> listPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class, wrapper);
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}
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}
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```
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对应sql
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```
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SELECT
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t.id, t.name, t.sex, t.head_img,
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t1.tel, t1.address AS userAddress,
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t2.province, t2.city
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FROM
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user t
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LEFT JOIN user_address t1 ON t1.user_id = t.id
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LEFT JOIN area t2 ON t2.id = t1.area_id
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WHERE (
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t.id = ?
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AND t1.tel LIKE ?
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AND t.id > ?)
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```
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说明:
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* UserDTO.class 查询结果返回类(resultType)
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* selectAll() 查询指定实体类的全部字段
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* select() 查询指定的字段,支持可变参数,同一个select只能查询相同表的字段
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* selectAs() 字段别名查询,用于数据库字段与业务实体类属性名不一致时使用
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* leftJoin() 参数说明
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第一个参数: 参与连表的实体类class
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第二个参数: 连表的ON字段,这个属性必须是第一个参数实体类的属性
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第三个参数: 参与连表的ON的另一个实体类属性
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* 默认主表别名是t,其他的表别名以先后调用的顺序使用t1,t2,t3....
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* 条件查询,可以查询主表以及参与连接的所有表的字段,全部调用mp原生的方法,正常使用没有sql注入风险
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#### 一对多查询
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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@Test
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void testResultMap() {
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MPJLambdaWrapper<UserDO> wrapper = new MPJLambdaWrapper<UserDO>()
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.selectAll(UserDO.class)
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//对多查询
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.selectCollection(AddressDO.class, UesrDTO::getAddressList)
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//对一查询
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.selectAssociation(AddressDO.class, UesrDTO::getAddress)
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.leftJoin(AddressDO.class, AddressDO::getUserId, UserDO::getId);
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List<UserDTO> dtoList = userMapper.selectJoinList(UserDTO.class, wrapper);
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//关于对多分页查询
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//由于嵌套结果方式会导致结果集被折叠，因此分页查询的结果在折叠后总数会减少，所以无法保证分页结果数量正确。
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}
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}
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```
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等效于ResultMap
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```xml
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<resultMap id="xxxxxxxx" type="com.github.yulichang.join.dto.UserDTO">
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<result property="id" column="id"/>
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<result property="name" column="name"/>
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<!--其他属性省略-->
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<collection property="addressList" javaType="java.util.List"
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ofType="com.github.yulichang.join.entity.UserAddressDO">
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<id property="id" column="mpj_id"/>
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<result property="address" column="address"/>
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<result property="userId" column="user_id"/>
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<!--其他属性省略-->
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</collection>
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</resultMap>
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```
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MPJLambdaWrapper其他功能
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* [一对一，一对多使用](https://gitee.com/best_handsome/mybatis-plus-join/wikis/MyLambdaWrapper/selectCollection()?sort_id=6509590)
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* [简单的SQL函数使用](https://gitee.com/best_handsome/mybatis-plus-join/wikis/selectFunc()?sort_id=4082479)
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* [ON语句多条件支持](https://gitee.com/best_handsome/mybatis-plus-join/wikis/leftJoin?sort_id=3496671)
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### String形式用法（MPJQueryWrapper）
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#### 简单的连表查询
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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void testJoin() {
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MPJQueryWrapper wrapper = new MPJQueryWrapper<UserDO>()
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.selectAll(UserDO.class)
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.select("addr.tel", "addr.address", "a.province")
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.leftJoin("user_address addr on t.id = addr.user_id")
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.rightJoin("area a on addr.area_id = a.id")
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.like("addr.tel", "1")
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.le("a.province", "1");
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//列表查询
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List<UserDTO> list = userMapper.selectJoinList(UserDTO.class, wrapper);
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//分页查询 （需要启用 mybatis plus 分页插件）
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List<UserDTO> listPage = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class, wrapper);
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}
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}
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```
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对应sql
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```
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SELECT
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t.id,
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t.name,
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t.sex,
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t.head_img,
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addr.tel,
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addr.address,
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a.province
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FROM
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user t
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LEFT JOIN user_address addr on t.id = addr.user_id
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RIGHT JOIN area a on addr.area_id = a.id
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WHERE (
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addr.tel LIKE ?
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AND a.province <= ?)
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```
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说明:
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* UserDTO.class 查询结果类(resultType)
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* selectAll(UserDO.class) 查询主表全部字段(主表实体类)默认主表别名 "t"
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* select() mp的select策略是覆盖,以最后一次为准,这里的策略是追加,可以一直select
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主表字段可以用lambda,会自动添加表别名,主表别名默认是 t ,非主表字段必须带别名查询
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* leftJoin() rightJoin() innerJoin() 传sql片段 格式 (表 + 别名 + 关联条件)
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* 条件查询,可以查询主表以及参与连接的所有表的字段,全部调用mp原生的方法,正常使用没有sql注入风险
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#### 还可以这么操作,但不建议
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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void testJoin() {
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List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
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new MPJQueryWrapper<UserDO>()
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.selectAll(UserDO.class)
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.select("addr.tel", "addr.address")
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//行列转换
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.select("CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex")
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//求和函数
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.select("sum(a.province) AS province")
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//自定义数据集
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.leftJoin("(select * from user_address) addr on t.id = addr.user_id")
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.rightJoin("area a on addr.area_id = a.id")
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.like("addr.tel", "1")
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.le("a.province", "1")
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.orderByDesc("addr.id"));
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}
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}
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```
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对应sql
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```
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SELECT
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t.id,
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t.name,
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t.sex,
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t.head_img,
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addr.tel,
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addr.address,
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CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex,
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sum(a.province) AS province
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FROM
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user t
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LEFT JOIN (select * from user_address) addr on t.id = addr.user_id
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RIGHT JOIN area a on addr.area_id = a.id
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WHERE (
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addr.tel LIKE ?
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AND a.province <= ?)
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ORDER BY
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addr.id DESC
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```
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# [wiki](https://gitee.com/best_handsome/mybatis-plus-join/wikis)
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