mybatis plus 左连接

MyBatis Plus提供了API来支持左连接查询。可以使用leftJoin方法进行左连接操作。要使用MyBatis Plus的左连接功能，首先确保你使用的是MyBatis Plus的最新版本，并且已经正确导入了相关的依赖。你可以在MyBatis Plus的官方文档或GitHub仓库中查找最新的版本信息。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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相关问题

mybatis-plus左连接

MyBatis-Plus is a widely used Java persistence framework that extends the capabilities of MyBatis. It provides additional features and utilities to simplify database operations. To perform a left join using MyBatis-Plus, you can use the `leftJoin()` method provided by the `QueryWrapper` class.

Here's an example of how to perform a left join using MyBatis-Plus:

// Assuming you have two entities: User and Order

// Create a QueryWrapper object for the User entity
QueryWrapper<User> queryWrapper = new QueryWrapper<>();

// Perform a left join with the Order entity using the column names for the join condition
queryWrapper.leftJoin("order", "user.id = order.user_id");

// Execute the query
List<User> userList = userMapper.selectList(queryWrapper);

In this example, `user` and `order` are the table names, `user.id` and `order.user_id` are the column names used for the join condition. The `selectList()` method will return a list of `User` objects containing the joined data.

Please note that this is just a basic example, and the actual implementation may vary depending on your database schema and mapping configurations.

mybatis plus怎么自定义左连接sql

你可以使用Mybatis-plus提供的Wrapper作为左连接的条件，例如：

List<User> userList = userMapper.selectList(
    new QueryWrapper<User>()
        .leftJoin("user_info", "user_info.user_id=user.id and user_info.age>18")
        .select("user.*, user_info.age as age")
);

这个例子中，我们使用leftJoin方法定义了一个左连接，左连接的条件是`user_info.user_id=user.id and user_info.age>18`，同时查询返回的结果包括user表的全部字段以及user_info表的age字段（注意，本例需要在User类中定义一个名为age的属性）。

需要注意的是，`leftJoin`方法中第一个参数是左连接的表名，第二个参数是左连接的条件，条件格式为SQL语句，可以在其中引用已经定义的表别名，例如本例中的`user_info.user_id`。同时，在选择要查询的列时，也需要给别名加上表名前缀，例如本例中的`user_info.age as age`。

希望这个例子能够帮助你自定义Mybatis-plus的左连接SQL。