How do I prevent repeated values from being input in an Excel column?

1. Open the excel file to be processed, and select the columns to restrict duplicate items, as shown in the figure.

2. Find "menu bar-data validity", as shown in the figure below, the data validity dialog box is displayed.

 
3. Click the Settings tab. The default valid condition is "allow" and "allow. Select custom from the drop-down list (. At the same time, enter = COUNTIF ($ C $2: $ C $27, C2) in the formula line. <2 the specific data depends on the selected region of the individual.

4. Click back to return to the Excel worksheet. In cell C14, which is about to enter data, try to enter the content of C13. Now we try to enter the repeated value to see if it is an invalid value.