Your pipeline includes a sort, but your output clearly is not sorted???

So, assuming that the output does not need to be sorted, we can replace the rest of the pipeline with a single invocation of awk:

Code:

filedate=$(date '+%d%m%Y')
awk '
/H\|/ {	pn[substr($0, 9, 18)]
}
END {	print "select * from tablename where sdigits in"
	sep = "("
	for(i in pn) {
		printf("%s%s", sep, i)
		sep = ",\n"
	}
	print ")"
}' $filedate*lpn*

But, of course, since no sample input was provided, the above code is completely untested. If, despite your sample output, you really do need the output to be sorted, you can modify the for loop in the END clause in the above awk code to feed the list to sort and feed the output from sort into another for loop to print the results. Or, the awk available on some systems provides a function that could be used to sort the pn[] array before printing the results.

And, you haven't told us what operating system or shell you're using. If you're using a Solaris/SunOS system, change awk in the above code to /usr/xpg4/bin/awk or nawk.