I might be doing this wrong but I named my groups numbers, so "7", "8" and "9" are separate groups. When I used the Dunn Test code, the Col Mean-Row Mean for "Group 8 mean-Group 8 mean" is 0.382100 with a p-value of 1.0000 (shown below). Would would the Dunn Test give me the z-score for a group subtracted by itself?

Dunn's Pairwise Comparison of rating by outcome (Bonferroni)

Code:
Col Mean-

Row Mean 7 8

8 -3.883837 0.382100

0.0019 1.0000

9 -3.829106 0.054730

0.0023 1.0000