Question

how do I get the fields of a column that’s without a match in another column?

I tried:

SELECT table1.page_title 
FROM table1, table2 
WHERE table1.page_title != table2.page_title

It produces a lot of duplicate fields so I did a:

SELECT DISTINCT table1.page_title 
FROM table1, table2 
WHERE table1.page_title != table2.page_title

but it just hangs.

Any help would be greatly appreciated, thanks!

P.S.
I’m doing this so I could create an exclude list for mediawiki’s MWDumper tool. I need it so that when I import the outputted sql, my current wiki entries will not be overwritten.

EDIT:
Yes they’re 2 different tables. Each has about 70,000+ records
Also why are my queries slow? I’d appreciate it if someone could clarify so I could learn why 🙂 Thanks again!

Answer 1

Are a and b different tables, both having a “page_title” column?

If so, try this:

SELECT DISTINCT page_title FROM a
WHERE page_title NOT IN (SELECT page_title FROM b)

If all you’re interested in is removing duplicates (if you only have one table), then there are several ways to do it, two of which are:

SELECT DISTINCT page_title FROM a

or

SELECT page_title FROM a
GROUP BY page_title

The GROUP BY option is stronger albeit slower – you can add a HAVING clause to choose only those titles that appear e.g. more than twice:

SELECT page_title FROM a
GROUP BY page_title
HAVING COUNT(page_title) > 2

Hope that helps

(Thanks Aaron F for the comment)