how can I update some table rows using data from existing rows?

Question

I have created a table where it stores some multilingual store data with this structure

create table store_locator_store_lang
(
    id_store int(11) unsigned not null,
    lang_id int not null,
    partner varchar(100) null,
    address varchar(255) null,
    city varchar(100) null,
    occupation varchar(100) null,
    primary key (id_store, id_lang)
);

id_lang can be 1 or 2

In there I have some incomplete data meaning that there are all the rows for lang_id = 1 but for lang_id = 2 many rows contain empty values.

I would like to populate the empty rows for lang_id = 2 with data from the rows with lang_id = 1.

The store entity is identified by id_store so the id_store is common for the two languages of the same store.

There is always a pair stored even if one row has empty columns. There is no chance there is a row missing for lang_id=2

Is it possible to accomplish this task with an update query in the database or do I have to export the data, edit and reinsert?

The Database server is 10.1.44-MariaDB-0ubuntu0.18.04.1 Ubuntu 18.04

Here's a dump of some example data

INSERT INTO store_locator_store_lang (id_store, lang_id, partner, address, city, occupation) VALUES (543, 1, 'TEST', 'TEST, Τ.Κ. 52100', 'TEST', 'TEST');
INSERT INTO store_locator_store_lang (id_store, lang_id, partner, address, city, occupation) VALUES (543, 2, '', '', '', '');

Answer 1

In general (if "many rows contain empty values" means "they contains NULL"):

UPDATE store_locator_store_lang t1
  JOIN store_locator_store_lang t2 ON t1.id_store = t2.id_store 
                                  AND t1.lang_id = 1
                                  AND t2.lang_id = 2
SET t2.partner = COALESCE(t2.partner, t1.partner),
    t2.address = COALESCE(t2.address, t1.address),
    t2.city = COALESCE(t2.city, t1.city),
    t2.occupation = COALESCE(t2.occupation, t1.occupation);

The empty value seems to be zero-length string and not null.

UPDATE store_locator_store_lang t1
  JOIN store_locator_store_lang t2 ON t1.id_store = t2.id_store 
                                  AND t1.lang_id = 1
                                  AND t2.lang_id = 2
SET t2.partner = CASE WHEN t2.partner = ''
                      THEN t1.partner
                      ELSE t2.partner END,
    t2.address = CASE WHEN t2.address = ''
                      THEN t1.address 
                      ELSE t2.address END,
    t2.city = CASE WHEN t2.city = ''
                   THEN t1.city 
                   ELSE t2.city END,
    t2.occupation = CASE WHEN t2.occupation = ''
                         THEN t1.occupation 
                         ELSE t2.occupation END
/* WHERE '' IN (t2.partner, t2.address, t2.city, t2.occupation) */
    ;