Question

Say that I have a table with one column named CustomerId.
The example of the instance of this table is :

CustomerId
14
12
11
204
14
204

I want to write a query that counts the number of occurences of customer IDs.
At the end, I would like to have a result like this :

CustomerId      NumberOfOccurences
14              2
12              1
11              1
204             2
14              1

I cannot think of a way to do this.

Answer 1

This is the most basic example of GROUP BY

SELECT CustomerId, count(*) as NumberOfOccurences
    FROM tablex GROUP BY CustomerId;