sql - how to exclude rows that have duplicates in one field -

i have simple task, cannot find solution. have 2 tables, 'articles' , 'categories'

my article table this:

id | cat_id | title | content 1      1      blah     content 1 2      1      blah2    content 2 3      2      blah3    content 3 

my categories table this:

id | title 1     category 1 2     category 2 

you see have 2 articles have same cat_id. not want duplicate cat_id field. cannot use distinct, because articles, because want fields out.

so if use distinct this:

select distinct a.id, a.cat_id, a.title, a.content articles a

i out, want output this

id | cat_id | title | content 2      1      blah2    content 2 3      2      blah3    content 3 

can me please !!!

this query select first article (lowest id) each category

select a.* article left join     article a2 on a.id<a2.id , a.cat_id=a2.cat_id a2.id null 

it outer join other articles. join clause joins articles same category , smaller id. when there no matches (a2.id null), have article lowest id category.