The aggregate, or aggregation functions, initially appear inside the
SELECT clause of a query, and they perform computations over sets of values in multiple rows of our relations. The basic aggregation functions supported by every SQL systems are:
Now that the aggregation functions have been introduced, two new clauses can be added to the SQL select statements. These are the:
GROUP BY, and the
GROUP BY allows us to partition our relations into groups, and then compute aggregated aggregate functions over each group independently.
HAVING condition allows us to test filters on the results of aggregate values.
The difference between the
HAVING conditions is the
HAVING applies to all the groups generated from the
GROUP BY clause. While the
WHERE condition applies to single rows at a time.
The syntax looks like this:
SELECT A1, A2, . . . , A(n)FROM R1, R2, . . . , R(m)WHERE <condition>GROUP BY <columns>HAVING <condition>;