使用两列选择唯一计数

Question

I have a table with two columns of interest: apc and tid . The same apc can be in a row with multiple tid s, and an apc - tid pair can appear multiple times in the database (with different timestamps).

I want to get the apc s with a count of how many unique tid s they match with. So for:

apc        tid
---------------
abc        012
abc        012
abc        322
def        322
def        432
def        000

I want to get:

apc        count
-----------------
abc          2
def          3

I tried doing a group by on apc and tid , but I get all of the duplicates as unique counts (so 3 and 3 above). I tried throwing in distinct in a few places, but that didn't work either.

Answer 1

You need to do a Count(Distinct tid) :

Select  apc, Count(Distinct tid) as Count
From    Table
Group by apc