Bash/awk: when pattern not present print "not present" only once, not per line

I am searching for a pattern in a field of my file with several rows. If the pattern is present I would like to output that row. However, if the pattern is not present at all I would like to output something like "missing".

awk '{if($2=="123456"){print $0} else {print "not present"} }' file.txt

(this does not work due to line by line output)

My problem is the line by line output here. There is one output per line, but I want either the row that matches the pattern or the term "missing" (only once).

I appreciate every kind of help! I tried several approaches including grep, if else, loops, but nothing works as I want.