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https://gitee.com/best_handsome/mybatis-plus-join
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299 lines
8.3 KiB
Markdown
299 lines
8.3 KiB
Markdown
# mybatis-plus-join
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* 支持连表查询的[mybatis-plus](https://gitee.com/baomidou/mybatis-plus)
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* [演示示例](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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1. 在项目中添加依赖
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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>1.1.6</version>
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</dependency>
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```
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- Gradle
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```
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implementation group: 'com.github.yulichang', name: 'mybatis-plus-join', version: '1.1.6'
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```
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或者clone代码到本地自行安装,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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1. MPJBaseMapper继承BaseMapper,在原有的方法基础上又添加了以下方法:
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* selectJoinOne 连表查询一条记录对象
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* selectJoinList 连表查询返回命中记录对象集合
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* selectJoinPage 连表分页查询对象集合
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* selectJoinMap 连表查询一条记录返回Map
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* selectJoinMaps 连表查询返回命中记录Map集合
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* selectJoinMapsPage 连表分页查询返回Map集合
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2. MPJBaseService 继承了IService,同样添加以上方法
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3. MPJBaseServiceImpl 继承了ServiceImpl,同样添加了以上方法
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## 核心类 MPJLambdaWrapper和MPJQueryWrapper
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### MPJLambdaWrapper用法
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#### MPJLambdaWrapper示例
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#### 简单的3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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List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
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new MPJLambdaWrapper<UserDO>()
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.selectAll(UserDO.class)
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.select(UserAddressDO::getTel)
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.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
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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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}
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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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t1.tel,
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t1.address AS userAddress,
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t2.province,
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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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故将UserAddressDO和AreaDO分开为两个select()
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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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#### 分页查询
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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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IPage<UserDTO> iPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class,
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new MPJLambdaWrapper<UserDO>()
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.selectAll(UserDO.class)
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.select(UserAddressDO::getTel)
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.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
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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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}
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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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t1.tel,
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t1.address AS userAddress,
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t2.province,
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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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LIMIT ?,?
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```
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### MPJQueryWrapper
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#### 简单的3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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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", "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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}
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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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#### 分页查询
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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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IPage<UserDTO> page = userMapper.selectJoinPage(new Page<>(1, 10), 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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.select("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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}
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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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LIMIT ?,?
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```
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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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