Need SQL to return all rows where C1 occurs more than once, C1 is duplicated, AND, C2 contains different values.
In this example, the AAA rows and CCC rows would be rendered; they meet the above criteria:
C1 C2
AAA 123
AAA 456
BBB 333
BBB 333
CCC 788
CCC 788
CCC 891
DDD 555
BT