How can I append a string to an existing field in MySQL?

I want to update the code on all my record to what they currently are plus _standard any ideas?

So for example if the codes are apple_1 and apple_2 I need them to be apple_1_standard and apple_2_standard

Before:

id   code
------------
1    apple_1 
1    apple_2

Psuedo Query:

update categories set code = code + "_standard" where id = 1;

Expected result:

id   code
----------------------
1    apple_1_standard 
1    apple_2_standard

You need to use the CONCAT() function in MySQL for string concatenation:

UPDATE categories SET code = CONCAT(code, '_standard') WHERE id = 1;

Update image field to add full URL, ignoring null fields:

UPDATE test SET image = CONCAT('https://my-site.com/images/',image) WHERE image IS NOT NULL;