Awk with or and not operator

Shell Programming and Scripting
1 
awk -F '/' '{ if (($2!="30") print }' f.dat > date_mismatch.dat

The above command is giving the desired results

But I would want use Or in the above but it is returning the complete file

awk -F '/' '{ if ($2!="30"||$2!="31") print }' f.dat > date_mismatch.dat

Have tried the braces,spacing,quotes but with no use...Any quick help...

I would want this to be in awk

Is there a way of using something like an IN operator

---------- Post updated at 10:25 AM ---------- Previous update was at 10:10 AM ----------

Thanks was able to do using the following

awk 'BEGIN {OFS=FS="/"; } $2 !~ /30|31|28/' f.dat > date_mismatch.dat
2

Try

awk -F '/' '{ if ($2!="30" && $2!="31") print }' f.dat > date_mismatch.dat

or

awk -F '/' '{ if !($2="30" || $2="31") print }' f.dat > date_mismatch.dat