Excel2003 to prevent repetitive data entry techniques

Excel2003 to prevent repetitive data entry techniques

① Select the range of cells (such as D3 to D14 columns) where you want to enter your ID number.

② click data → effectivity to open the Data Validation dialog box.

③ Open the Data Validation dialog box, under the Settings tab, press the Drop-down button to the right of allow.

④ in the shortcut menu that pops up, select the Custom option, and then enter the formula in the formula box below: =countif (D:D,D3) = 1, OK to return. When you enter a duplicate ID number in the cell above, the prompt dialog box pops up and the number you enter is rejected.