I have a table of students:
id | age
--------
0 | 25
1 | 25
2 | 23
I want to query for all students, and an additional column that counts how many students are of the same age:
id | age | count
----------------
0 | 25 | 2
1 | 25 | 2
2 | 23 | 1
What’s the most efficient way of doing this? I fear that a sub-query will be slow, and I’m wondering if there’s a better way. Is there?
