Counting occurrences in SQL

I have following table structure:

Student   School Code   Roll Number
A           12            135
B           12            248
C           16            934
D           16            437
E           12            249

I want to get the count of students in one school code and display the count. I can do a row_number and get the number of rows in this way:

select student, School code, 
row_number() over(partition by School Code order by Roll Number) AS line_no
from table ;

the output would be:

Student   School Code   line_no   Total_Count
A            12           1          3
B            12           2          3
E            12           3          3
D            16           1          2
C            16           2          2

I am not able to write the sql code to produce the last column (i.e Total_Count). Can you please tell me how to do it.

Answer

You want the count() window function:

select student, School code, 
       row_number() over(partition by School Code order by Roll Number) as line_no
       count(*) over(partition by School Code) as total_count
from table ;