learn Basic Structure of SQL

- SQL is based on set and relational operations with certain modifications and enhancements
- A typical SQL query has the form:
select A1, A2, ..., An
from r1, r2, ..., rm
where P
• Ais represent attributes
• ris represent relations
• P is a predicate.
-This query is equivalent to the relational algebra (to be
discussed later) expression ∏A1, A2, ..., An(σP (r1 x r2 x ... x
rm))
- The result of an SQL query is a relation.