这就是最终对我起作用的原因：
首先，我从初始数据库中提取级别，因此：

INSERT INTO db2.levels(`name`,`school_id`,`short_code`)
SELECT name ,school_id,short_code
FROM db1.levels 
GROUP BY name 
ORDER BY  CAST(IF(REPLACE(name,' ','')='','0',REPLACE(name,' ','')) AS UNSIGNED 
INTEGER) ASC;

然后我为类插入创建了一个过程

CREATE PROCEDURE dowhileClasses()
BEGIN
SET @Level = 1;
SET @Max = SELECT count(`id`) FROM  db2.levels;
START TRANSACTION;
WHILE @Level <= @Max  DO
    BEGIN
         DECLARE val1 VARCHAR(255) DEFAULT NULL;
         DECLARE val2 VARCHAR(255) DEFAULT NULL;
         DECLARE bDone TINYINT DEFAULT 0;
         DECLARE curs CURSOR FOR 
            SELECT trim(`Class1`)
            FROM db1.dbo_tblstudent 
            WHERE CAST(IF(REPLACE(name,' ','')='','0',REPLACE(name,' ','')) AS UNSIGNED INTEGER) =@Level
            GROUP BY `Class1`;
         DECLARE CONTINUE HANDLER FOR NOT FOUND SET bDone = 1;
         OPEN curs;
         SET bDone = 0;
         REPEAT
            FETCH curs INTO val1;
            IF bDone = 0 THEN 
                SET @classname = val1;
                SET @levelID = (SELECT id FROM db2.levels WHERE short_code=@Level limit 1);
                SET @schoolId = 1;
                    SET @classId = (SELECT `id` FROM db2.classes where class_name = @classname and level_id= @levelID limit 1);

                    IF @classId is null and @classname is not null THEN
                        INSERT INTO db2.classes(class_name,school_id,level_id)
                            VALUES(@classname,@schoolId,@levelID);
                    END IF;
                END IF;
         UNTIL bDone END REPEAT;
         CLOSE curs;
    END;
     SELECT CONCAT('lEVEL: ',@Level,' Done');
    SET @Level = @Level + 1;
  END WHILE;
END;
//

delimiter ;

CALL dowhileClasses();

有了这个，我就可以扔掉 classes 与先前创建的 level_id s。
整个魔法依赖于 CURSOR 协议。
关于更多细节，这里是我使用的文档之一。

尝试为“已处理”添加列，然后执行while exists循环

INSERT INTO db2.levels(level_name,X,Y)
SELECT class_name as level_name,1 as X,ClassAdmitted as Y, 0 as Processed
FROM db1.stdlist
GROUP BY ClassAdmitted;

WHILE EXISTS(SELECT * FROM db2.levels WHERE Processed = 0)
BEGIN 
DECLARE @level_name AS VARCHAR(MAX)
 SELECT TOP 1 @level_name=level_name FROM db2.levels WHERE Processed = 0
--YOUR CODE
UPDATE db2.levels SET Processed=1 WHERE level_name=@level_name

END

您可能需要先转储到temp表中，然后在完成处理后插入到实际表（db2.levels）中。这样就不需要在最后一个表上处理不必要的列。