1. Type the following formula in cell B1:
=IF(ISERROR(MATCH(A1,$G$1:$G$150,0)),"","Match in Col G")
2. Select cells B1:B150
3. Then "Edit", select "Fill" on the Edit menu, and then click “Down”.
This will compare Column A against Column G and insert the comment
"Match in Col G" next to the data in Column A matched in Column G.
The columns do not have to be sorted, although it might be easier.
I Started at Row 1, change the formula if needed.
I used only 150 rows to check, again change if needed.