Filling foreign key values of a table through loop

I am trying to copy data from one table to another schema. But while copying the content I am struggling to fill foreign key values in the second database. Let's say the table (from which I'm trying to copy the data) is-

Sample_

Now, I have created another schema which has 3 tables:

main_

V3_

V4_

I have filled V3_, and V4_ but I haven't been able to fill main_ because of an error. I'm using loop to fill the values. I have ran the following code.

CREATE PROCEDURE ROWPERROW()
BEGIN
    DECLARE n INTEGER DEFAULT NULL;
    DECLARE i INTEGER DEFAULT NULL;
    SELECT COUNT(*) FROM sample_ INTO n;
    SET i=0;
    WHILE i<n DO
      INSERT INTO main_(v1, v2) SELECT (v1, v2) FROM sample_ LIMIT i,1;
      INSERT INTO main_(v3) SELECT v3_id FROM V3_ WHERE V3_.v3=SELECT v3 FROM sample_ LIMIT i, 1;
      INSERT INTO main_(v4) SELECT v4_id FROM V4_ WHERE V4_.v4=SELECT v4 FROM sample_ LIMIT i, 1;
      SET i = i + 1;
    END WHILE;
End;
;;

Error message:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT v3 FROM sample_ LIMIT i, 1; INSERT INTO main_(v4) SELECT v4_id FRO' at line 9

I don't understand why it is showing syntax error. Also, is there a better way to copy data from a one schema to another?

I want main_ to look like this-

main_