Tables represent a  format of rows and columns which define an entity or an object. 
Tables in SQL differ from relations in formal relational model, in that 
SQL allows a table to have two or more tuples that are identical in all their attribute 
values. Hence in general an SQL table is not a set of tuples, because a set does not 
allow two identical members ;rather it is a multiset of tuples. Some SQL relations are 
constrained to be sets because a key constraint has been declared or because the DISTINCT 
option has been used with the SELECT statement. We should be aware of this distinction.
to query and manipulate the information in the database, we
SELECT
UPDATE
INSERT
DELETE
CREATE VIEW