mybatisplus insert into select

MyBatis-Plus提供了两种方式实现Insert-Select操作：

1. 使用Wrapper进行构造SQL语句

QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.select("id", "name", "age")
        .eq("deleted", 0)
        .orderByDesc("age")
        .last("limit 10");
String sql = "insert into user (id, name, age) " +
        "select id, name, age from user_copy " +
        queryWrapper.getSqlSegment();
int result = userMapper.insert(new User(), new InsertIntoSelectInjector(sql));

2. 使用@Insert注解执行原生SQL

@Insert("insert into user (id, name, age) " +
        "select id, name, age from user_copy " +
        "where deleted = 0 order by age desc limit 10")
int insertBySelect();

其中，InsertIntoSelectInjector是一个自定义的Injector实现，用于执行原生SQL。可以参考以下代码：

public class InsertIntoSelectInjector extends AbstractSqlInjector {

    private final String sql;

    public InsertIntoSelectInjector(String sql) {
        this.sql = sql;
    }

    @Override
    public SqlNode inject(SqlNode sqlNode) {
        return new InsertIntoSelectNode(sql);
    }

    private class InsertIntoSelectNode extends AbstractSqlNode {

        private final String sql;

        public InsertIntoSelectNode(String sql) {
            this.sql = sql;
        }

        @Override
        public boolean apply(DynamicContext context) {
            context.appendSql(sql);
            return true;
        }
    }
}

注意，这种方式需要注意SQL注入的安全问题，建议使用第一种方式。