How can I easily INSERT data in a table from multiple columns from another table?

Question

I want to take all phone numbers from the companies table, and put that in a dedicated phone numbers table, is there an easy way to do this using (if possible) only one query?

example data from the companies table (tel3 and tel4 could have phone numbers):

id	tel	tel2	tel3	tel4
1	32772373636	32724522341
2	32783675626
3	32968381949

expected example output in phonenrs table:

id	company_id	phonenr
1	1	32772373636
2	1	32724522341
3	2	32783675626
4	3	32968381949

Answer 1

You could use an insert-select statement from a query that union alls the phone numbers:

INSERT INTO numbers (company_id, phonenr)
SELECT id, tel FROM numbers WHERE tel IS NOT NULL
UNION ALL
SELECT id, tel2 FROM numbers WHERE tel2 IS NOT NULL
UNION ALL
SELECT id, tel3 FROM numbers WHERE tel3 IS NOT NULL
UNION ALL
SELECT id, tel4 FROM numbers WHERE tel4 IS NOT NULL