Join queries combine data from two or more tables in a database. An inner join returns rows where there is a match between columns in both tables. A left join returns all rows from the left table, along with matched rows from the right table, returning null if there is no match. A right join is similar but returns all rows from the right table. A full join returns all rows and fills in nulls for missing matches between the tables.

1. Prepared by
Aftab Alam
Ashfaq Ahmad
Waqar Ali
Join Query

2. What is Join Query?
• Join is used to combine records from two
or more tables in a database.
• In database Join means combining fields
from two tables by using values common
to each.
• The data which is fetch from two or more
tables, is appear as single set of data.

3. Syntax
• Simple Join Query :
SELECT ColumnName_list from table1,table2
WHERE
table1.col = table2.col;
But it is old version.
• Simple join is also called inner join. but the syntax of inner join is
different, Both work same as simple query does.
SELECT ColumnName_list from table1
INNER JOIN
table2 ON table1.col = table2.col;
• It is also recommended syntax by Oracle.

4. Example
• Consider two tables CUSTOMER and ORDER
• CUSTOMER
In customer table we have three columns.
Customer_id
name
age.
• ORDER
In ORDER table we have
order_id
order_date
customer_id
amount number
• customer_id is common in both tables. And also we can use it for
relationship between these two tables.

5. Customer and Order tables
• In customer table we have following data
• In orders table we have following data

6. Joining tables
To joining the previous two tables
• We use the following queries:
Old:
select order_id, name, order_date, amount
from customer, orders
WHERE
customer.customer_id = orders.customer_id;
Recommend:
select order_id, name, order_date, amount
from customer
INNER JOIN orders on
customer.customer_id = orders.customer_id;

7. Types of Join Query
1.Inner Join
2.Left Join
3.Right Join
4.Full Join
There are also more types of join
but we will discuss only the above
types

8. Inner Join
• It selects all rows from both tables when
there is a columns and its values match
between two tables.
• In other words it returns rows when
there is a match in both tables.
Syntax:
SELECT column_name(s)
FROM table1
INNER JOIN table2 ON
table1.column_name=table2.column_name;

9. Inner Join Example
• Query
Select * from customer
inner join orders on
customer.customer_id = orders.customer_id;

10. Left Join
• It returns all rows from the left table (table1),
with the matching rows in the right table
(table2). The result is NULL in the right side
when there is no match.
• In other words it returns all rows from the left
table, even if there are no matches in the
right table.
Syntax:
SELECT column_name(s)
FROM table1
LEFT JOIN table2 ON
table1.column_name=table2.column_name;

11. Left Join Example
• Query
Select * from customer
left join orders on
customer.customer_id = orders.customer_id;

12. Right Join
• The RIGHT JOIN keyword returns all rows
from the right table (table2), with the
matching rows in the left table (table1). The
result is NULL in the left side when there is no
match.
• In other words returns all rows from the right
table, even if there are no matches in the left
table.
Syntax:
SELECT column_name(s)
FROM table1
RIGHT JOIN table2 ON
table1.column_name=table2.column_name;

13. Right Join Example
• Query
Select * from customer
right join orders on
customer.customer_id = orders.customer_id;

14. Full Join
• It combines the results of both left and right
table.
• The joined table will contain all records from
both tables, and fill in NULLs for missing
matches on either side.
Syntax:
SELECT column_name(s)
FROM table1
FULL JOIN table2 ON
table1.column_name=table2.column_name;

15. Full Join Example
• Query
Select * from customer
full join orders on
customer.customer_id = orders.customer_id;