Need Help with Complicated WHERE Clause

Here's my SELECT statement:

SELECT

adv,
advlogo,
advurl,

cat,
caturl,

instr,
blockanch,

anch,
gotourl,
code,
DATE_FORMAT(expdate, '%d %M, %Y') AS formated_date,

expun

FROM tadv, tcat, tinstr, tcoupon

LEFT JOIN texpun on tcoupon.expunid=texpun.expunid

WHERE 

tcoupon.advid=tadv.advid AND
tcoupon.catid=tcat.catid AND
tcoupon.instrid=tinstr.instrid;

Code (markup):

I want to add the following but it doesn't work:

AND type='a' || type='c';

Code (markup):

Funny thing is, it works without all the other WHERE clauses. For example:

SELECT * from tcoupon WHERE type='a' || type='c';

Code (markup):

Anyone know how to do it?

 

How about

where xxxx AND yyyy AND zzz AND (type='a' OR type = 'c')

 

Thanks, Onera! It worked.

I added reputation points to your account.