If statement to find matching values in columns in Excel

Excel -  I need to look at a list of IDs  find then in another column and then place an 'X' in another column if found.
Example

Look at column   AT   if you find a match in column   C   put a   X   in column  AL

Column C      Column AL      Column AT
123                           X                    123
123                           X                    345
456                                                  234
789                                                  567
987                                                  321
654
321                            x
321                            x
321                            x
ssblueCoordinatorAsked:
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irudykCommented:
Try the following formula in column AL

IF(ISNA(VLOOKUP(C1,AT$1:AT$5,1,FALSE)),"","X")

Change C1 to the correct row number (e.g. C2 or whatever the row number you are starting at)
Change AT$1:AT$5 to be the range you want to look for values in (e.g. if the lookup range starts at row 10 and goes to row 20 the formula would be AT$10:AT$20)
ssblueCoordinatorAuthor Commented:
I get an error about to many arguments

=IF(ISNA(VLOOKUP(C2,AT$2:AT$913),1,FALSE)),"","X")
irudykCommented:
This should read:

=IF(ISNA(VLOOKUP(C2,AT$2:AT$913,1,FALSE)),"","X")

I screwed up my initial post which I have since revised.

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ssblueCoordinatorAuthor Commented:
=IF(ISNA(VLOOKUP(C2,AT$2:AT$913,1,FALSE),"","X")

Still getting the same error?????
irudykCommented:
Sorry, I had a typo in my last response which I've since corrected. You need to add another closing bracket after the FALSE
ssblueCoordinatorAuthor Commented:
Got it!  Thanks!!
Subodh Tiwari (Neeraj)Excel & VBA ExpertCommented:
Another variation you may try is this...

=IF(ISNUMBER(MATCH(C2,AT:AT,0)),"X","")

Open in new window

OR simply this...
=IF(COUNTIF(AT:AT,C2),"X","")

Open in new window

Using VLookup for a single column table_array doesn't make much sense. All you need is to confirm whether a number exists in another column or not so in that case either you may use MATCH or COUNTIF function to confirm this.
ssblueCoordinatorAuthor Commented:
Thanks for comment and explanation.
Subodh Tiwari (Neeraj)Excel & VBA ExpertCommented:
You're welcome!
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