Concatenate several fields into one with SQL

Question

I have three tables tag, page, pagetag

With the data below

page

ID      NAME
1           


        

Answer 1

pagetag.id and group_concat(tag.name) will be null for page 4 in the example you've posted above, but the page shall appear in the results.

You can use the COALESCE function to remove the Nulls if you need to:

select COALESCE(pagetag.id, '') AS id ...

It will return the first non-null value from it's list of parameters.