Eager and Lazy Aggregation

Aggregate processing summarizes large amounts of data with an aggregated value.

Aggregate processing is one of the most useful operations in DBMS environments. It summarizes these values:
In SQL, aggregate processing is performed using the aggregation functions min(), max(), count(), sum(), and avg(), and group by and having clauses. The SQL language implements two aggregate processing types, vector aggregation and scalar aggregation. A select-project-join (SPJ) query illustrates these two types of aggregate processing:
select r1, s1
from r, s
where r2 = s2