Excel's Formula - sisman

Chapter 19: Conditional Formatting and Data Validation 551
This formula assumes that A2 is the active cell in the selected range. Note that you can’t use this
formula for a cell in row 1.
Accepting nonduplicate entries only
The following data validation formula does not permit the user to make a duplicate entry in the
range A1:C20:
=COUNTIF($A$1:$C$20,A1)=1
This formula assumes that A1 is the active cell in the selected range. Note that the first argument
for COUNTIF is an absolute reference. The second argument is a relative reference, and it adjusts
for each cell in the validation range. Figure 19-29 shows these validation criteria in effect, using a
custom error alert message. The user is attempting to enter 16 into cell B5.
Figure 19-29: Using data validation to prevent duplicate entries in a range.
Accepting text that begins with a specific character
The following data validation formula demonstrates how to check for a specific character. In this
case, the formula ensures that the user’s entry is a text string that begins with the letter A (either
upper- or lowercase).
=LEFT(A1)=”a”
This formula assumes that the active cell in the selected range is cell A1.