ALTER TABLE example ALTER COLUMN id TYPE text USING md5(id::TEXT)

ID| Firstname | Lastname
  |   Henry   |  Miles
  |   Bob     |  Cruz
  |   Chris   |  Chen
  |   Bob     |  Cruz
  |   Chris   |  Chen
  |   Lue     |  Jackson

ID                                | Firstname | Lastname
0000023f507999464aa2b78875b7e5d6  |   Henry   |  Miles
00000ce845c00cbf0686c992fc369df4  |   Bob     |  Cruz
00000f7264c27ba6fea0c837ed6aa0aa  |   Chris   |  Chen
00000ce845c00cbf0686c992fc369df4  |   Bob     |  Cruz
00000f7264c27ba6fea0c837ed6aa0aa  |   Chris   |  Chen
0000104cd168386a335ba6bf6e32219d  |   Lue     |  Jackson