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mysql> Select Count(Ecode) from Employee;

Output: 5 (No NULL value exists in the column Ecode.)
mysql> Select Count(Salary) from Employee;

Output: 3 (NULL values are ignored while counting the total number of records
on the basis of Salary. )
a. SQL JOINS

An SQL JOIN clause is used to combine rows from two or more tables, based on a common field
between them. While querying for a join, more than one table is considered in FROM clause.
The process/function of combining data from multiple tables is called a JOIN. SQL can extract
data from two or even more than two related tables by performing either a physical or virtual
join on the tables using WHERE clause. The types of SQL joins are as follows:

1. Cartesian Product (Cross Product)
2. Equi Join

3. Self Join
4. Non-Equi Join

5. Natural Join
12.18.1 Cartesian Product (Cross Product)

The Cartesian product is also termed as cross product or cross-join. The Cartesian product is a
binary operation and is denoted by (X). The degree of the new relation formed is the sum of the
degrees of two relations on which Cartesian product is performed. The number of tuples in the
new relation is equal to the product of the number of tuples of the two tables on which Cartesian
product is performed.
For example,

If A= {1,2,3} and B={a,b,c}, find A X B.
C = A X B
(1,a)
(1,b)
(1,c)
A B (2,a)
(2,b)
1 a (2,c)

(3,a)
2 X b = (3,b)
(3,c)
3 c

Cartesian Product for A X B

Table: student Table: games
Rollno Name gameno gname
1 Rohan 10 Football Relational Database and SQL
2 Jaya 11 Lawn tennis
3 Teena

12.47