Copying data in two tables with foreign keys - mysql

Question

I have two tables, reviews and grade.
Reviews table has
id_review (primary key), id_lang, email, text etc.
Example
1, 2, email#email.com, test text
2, 2, email#email.com, test text
4, 2, email#email.com, test text
Grade table has
id_review (primary/foreign key), id_criterion, grade
1, 3, 5.00
1, 1, 4.00
2, 3, 3.00
2, 1, 5.00
4, 2, 3.00
I need to copy all the reviews with lang id 2, change the text and the lang id to 1 (this I can do manually).
But as the id_review changes with the copied reviews, I need to create new rows on the grade table, too. Is there a way to make sure that the foreign keys are matched with the copied reviews, too?
I tried to do it the old fashioned way with copy/paste on csv but as some reviews are removed from the reviews table and some reviews have differences in id_criterion count, it's very hard to do for a large table.
Or should I try to edit the table to allow the reviews table to have distinct values for id_lang with the same id_review?

Answer 1

You can create temporary tables (no foreign keys) out of the original ones, patch and validate the data until you satisfy and then insert back to the original tables.
I am not sure how you populate id_review, so I assume they are auto generated when you insert new rows.
create table reviews_temp_20211119 as
select r.id_review as old_id_review
, 0 as new_id_review
, row_number() over(order by r.id_review) as ref_patch_id
, r.id_lang
, r.email
, r.text
from reviews r
where id_lang = 2;
create table grades_temp_20211119 as
select g.id_review
, g.id_criterion
, g.gradate
, 0 as new_id_review
from grades g
where g.id_review in (select t.old_id_review from reviews_temp_20211119 t);
update reviews_temp_20211119
set id_lang = 1;
alter table reviews add column ref_patch_id bigint null;
-- insert back to original to get the auto generated id_review
-- if you use other strategies to populate the id_review, you can do update it directly to the temp table and review if all the data are correct before insert back to the original table
insert into reviews (id_lang, email, text, ref_patch_id)
select id_lang, email, text, ref_patch_id
from reviews_temp_20211119;
update reviews_temp_20211119 t
join reviews r on (r.ref_patch_id = t.ref_patch_id)
set t.new_id_review = r.id_review;
update grades_temp_20211119 g
join reviews_temp_20211119 t on (g.id_review = t.old_id_review)
set g.new_id_review = t.new_id_review);
insert into grades (id_review, id_criterion, grade)
select t.new_id_review
, t.id_criterion
, t.grade
from grades_temp_20211119 t;
By keeping the temporary tables, you have opportunity to review or rollback the change if something went wrong by looking back at the temporary tables.

Answer 2

For a repeatable process, I think a stored procedure with cursors is the way. Here's my version, it accept two parameters, the old idLang you wish to copy, and the new idLang:
CREATE PROCEDURE copyReviewWithNewLang(IN oldidLang INT, IN newidLang INT)
BEGIN
DECLARE c_idReview, c_maxIdReview INT;
DECLARE c_text, c_email VARCHAR;
DECLARE old_c_idreview INT DEFAULT 0;
-- first cursor gets all the review rows of the old language, ordered
DECLARE rev_cur CURSOR FOR SELECT idReview, email, text FROM reviews WHERE id_lang = oldidLang ORDER BY idReview ASC;
-- second cursor gets the highest idReview
DECLARE maxid_cur CURSOR FOR SELECT MAX(idReview) FROM reviews;
-- needed for ending the loop on end of retrieved data
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN rev_cur;
retrieving : LOOP
FETCH rev_cur INTO c_idReview, c_email, c_text;
-- ending the loop
IF done THEN
LEAVE retrieving;
END IF;
IF (old_c_idreview = 0) OR (old_c_idreview != c_idReview) THEN
OPEN maxid_cur;
FETCH maxid_cur INTO c_maxIdReview;
CLOSE maxid_cur;
SET c_maxIdReview = c_maxIdReview + 1
END IF;
-- copying the review row
INSERT INTO reviews (id_review, id_lang, email, text)
VALUES(c_maxIdReview, newidLang, c_email, c_text)
-- copying the grade rows
INSERT INTO grades (id_review, id_criterion, grade)
SELECT c_maxIdReview, id_criterion, grade FROM grades
WHERE id_review = c_idReview;
-- needed for checking if id changed
SET old_c_idreview = c_idReview;
END LOOP;
CLOSE rev_cur;
END;