About aggregate functions in SQL
• AVG: Average of the column. If you want to get the average of marks for a student then you can use this function as
select avg(marks) as average marks
• COUNT: Number of records. If you want to count number students who has got >50 marks in maths
where marks>50 and subject='maths'
• MAX: Maximum of the column. If you want to find out who has got maximun marks in any subject then
• MIN: Minimum of the column. This is opposite to the max function
• SUM: Sum of the column. To find out total marks of a student
select sum(marks) as total
Other than aggregate functions we can write our own user defined functions which will do desired operation; so that we need not write the same logic again and again. For example, having a function to take a comma separated value as input and retuning a table as output with splitted values in each row.
SQL functions are precompiled and cached so they are pretty fast in run time.