When input data, in order to prevent duplication of entry (ID numbers are the same), the following settings
Selecting a first column, data validation data --- >> allows> Custom (ignore the null values preceding remove the check mark), a formula written in the block = COUNTIF (A: A, A2) = 1 set!
Mean function is: A: A within a range (range), A1 cell contents match the same grid and the number of counts (Criteria)
criteria can be anything, such as
Grid number in column D has two larger than D5.
Count "Shanxi XX" grid
Both have Beijing in Shanxi