I'm not sure whether you want to check for a duplicate on the corresponding row in Sheet A or whether any cell in Column A on Sheet A has the value in the corresponding row in Sheet B. I'm assuming your first sheet is named `Sheet1`

, the second sheet is named `Sheet2`

, and both data sets start on the first row of their sheet.

### Testing for duplicates in the entire column

Place `=IF(COUNTIF(Sheet1!A:A,B1)>0,"YES","NO")`

in A1 on Sheet2. It will say "YES" or "NO" depending on whether any cell in column A on Sheet1 has the value in B1 on Sheet2. Drag the cell down to adjust it for more rows.

How it works: `COUNTIF`

returns the number of cells in a range that satisfy a condition. The range `Sheet1!A:A`

includes all cells in column A of Sheet1. They are tested for equality with B1 (which will be adjusted when you drag the cell). The `IF`

function returns a value depending on the value of its condition, which is whether the number of cells from `COUNTIF`

is nonzero.

### Highlighting duplicates from the entire column

*Added in response to a comment.*

To highlight based on the presence of duplicates, conditional formatting needs to be applied. Click on the B column header in the second sheet to select the entire column, then choose Manage Rules under the Conditional Formatting button. Add a new rule with the type "Use a formula to determine which cells to format." Press the Format button to select what formatting will be applied. (Highlights can be done with the Fill tab.) Place `=(COUNTIF(Sheet1!A:A,B1)>0)`

in the formula box, then click OK.

### Testing for duplicates in the corresponding row

Place `=IF(Sheet1!A1=B1,"YES","NO")`

in A1 on Sheet2. Again, it says "YES" or "NO" and you can drag it down to more rows.

How it works: the `=`

between `Sheet1!A1`

(which refers to A1 on Sheet1) and `B1`

tests whether those cells' values are equal. `IF`

functions the same as above.