Joins

In this lesson we are going to study about joins in a database . In order to join rows from multiple table or view we use join in our statement in this session we will briefly discussing the join and type of join in database .
JOINS:

• Joins query are written in the where clause of the select statement.
• Joins condition :comparing two columns of two tables.
• Database engine joins the table according to the join condition .
• If we want to join more then two table then database engine evaluates columns of the two tables and then it joins the result to the other table.

Have a look this image which shows the operation of the join.

Table A and Table B is having some common columns .by giving the condition in where clause we can have the result of joined table.

NOTE: The columns which are using in join condition must have the same datatype . otherwise it will give error and to prevent this cause if having different datatype but still we want to use that columns in join condition then use the cast function to convert the datatype and then use in join condition .

Type of Joins:

 Joins are classified according to the different type way the join operation performed on the tables.

we will discuss about all this Join in details in the next section .
Related Article

• Cross Join 
• Equi Join
• Non  Equi Join
• Self Join 
• Natural Join 
• Join with Using clause.
• Join with ON clause
• Outer Join.  

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