Question

I have two MySQL database that contain two table, let’s call them TABLE_A and TABLE_B. Both these tables have as fields id and title. Both databases are on the same server and the same user can access both.

Now, TABLE_A is a subset of TABLE_B for what concern the title field. It means that every title in TABLE_A is present in TABLE_B, too. While id fields of the two table are in no way related.

What I need is to sync id fields in TABLE_A with id fields in TABLE_B, according to the title, i.e. same title, same id. If it’s not clear, I have to save TABLE_B id and override TABLE_A ones. And I DON’T have to add missing title from TABLE_B to TABLE_A.

Someone suggested to use a temporal table where to copy all TABLE_B fields in common with TABLE_A and then rename it as TABLE_A. I cannot follow this way, as TABLE_A actually has also other fields that I need to maintain. So, I cannot entirely drop the old TABLE_A.

Moreover, id is the primary key for both tables. It means that I cannot simply copy from TABLE_B to TABLE_A as the query will fail as soon as I try to change one id to another one that is already present in TABLE_A but linked to a different title.

I know how to write a Perl or PHP script to do it, but I would like to know if a pure MySQL solution exists.

Answer 1

You can do this

CREATE TABLE TableA_TMP AS
SELECT * FROM TableA;

ALTER TABLE TableA_TMP ADD id_new int;

UPDATE TableA_TMP A INNER JOIN TableB B ON lower(A.title) = lower(B.title)
SET id_new = B.id;

RENAME TABLE TableA TO TableA_backup;    

CREATE TableA AS
select id_new as id, title,.... from TableA_TMP;