DATABASE | SQL | SQL INTERVIEW QUESTION AND ANSWERS 4 | DEFINE JOINS? | WHAT ARE THE TYPES OF JOINS? | DEFINE EQUI JOINS? | DEFINE CARTESIAN JOIN? | WHAT ARE THREE SQL KEYWORDS USED TO CHANGE OR SET SOMEONE'S PERMISSIONS? | WHAT ARE PRIMARY KEYS AND FOREIGN KEYS?

Sql Interview Question and Answers:

19.     Define Joins?
      A Join combines columns and data from two or more tables (and in rare cases, of one table with itself).

20.     What are the types of Joins?
    Equi joins
    Cartesian Joins
    Outer Joins
    Self Joins.

21.     Define Equi Joins?
      A Equi Join is a join in which the join comparison operator is an equality. When two tables are joined together using equality or values in one or more columns, they make an Equi Join.

22.     Define Cartesian Join?
      Joining two tables without a whereclause produces a Cartesian join which combines every row in one table with every row in another table.

23.     What are three SQL keywords used to change or set someone's permissions?
      GRANT, DENY, and REVOKE

24.     What are primary keys and foreign keys?
      Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.

Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.