SQL Join – Interview Clear

http://www.sql-join.com/sql-join-types/

In below:  The relationship between the two tables is specified by the customer_id key, which is the “primary key” in customers table and a “foreign key” in the orders table:

customer_id first_name last_name email address city state zipcode
1 George Washington gwashington@usa.gov 3200 Mt Vernon Hwy Mount Vernon VA 22121
2 John Adams jadams@usa.gov 1250 Hancock St Quincy MA 02169
3 Thomas Jefferson tjefferson@usa.gov 931 Thomas Jefferson Pkwy Charlottesville VA 22902
4 James Madison jmadison@usa.gov 11350 Constitution Hwy Orange VA 22960
5 James Monroe jmonroe@usa.gov 2050 James Monroe Parkway Charlottesville VA 22902
order_id order_date amount customer_id
1 07/04/1776 $234.56 1
2 03/14/1760 $78.50 3
3 05/23/1784 $124.00 2
4 09/03/1790 $65.50 3

Note that (1) not every customer in our customers table has placed an order and (2) there are a few orders for which no customer record exists in our customers table.

Inner Join Query:

select first_name, last_name, order_date, amount
from customer
inner join orders
on customer.customer_id=orders.customer_id

Result:

first_name last_name order_date amount
george washington 07/04/1776 $234.56
john adams 05/23/1784 $124.00
Thomas Jefferson 03/14/1760 $78.50
Thomas Jefferson 09/03/1790 $65.50

 

 

 

 

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