Fast alternative to grep -f

Question

file.contain.query.txt

ENST001

ENST002

ENST003

file.to.search.in.txt

ENST001  90

ENST002  80

ENST004  50

Answer 1

If the files are already sorted:

join file1 file2

if not:

join <(sort file1) <(sort file2)