How to count instances in SQL

Question

I have a table like:

But I want to count the instances of my duplicate id's:

Any help would be appreciated.

Answer 1

This will be the syntax in MSSQL

 CREATE TABLE #test(id int , x1 int, x2 int)

 INSERT INTO #test(id,x1,x2) VALUES (1,1,1), (2,1,1), (2,2,2);

 SELECT id
        ,ROW_NUMBER() OVER(PARTITION BY id ORDER BY id)
        ,x1 
        ,x2
 FROM #test

Answer 2

Use ROW_NUMBER() function

SELECT id,
       ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS idcnt,
       x1,
       x2
  FROM tablename