Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 15 | Databases
15.2 What are the different types of joins? Please explain how they differ and why certain
types are better in certain situations.
SOLUTION
pg 80
JOIN is used to combine the results of two tables. To perform a join, each of the tables must
have at least one field which will be used to find matching records from the other table. The
join type defines which records will go into the result set.
Let’s take for example two tables: one table lists “regular” beverages, and another lists the
calorie-free beverages. Each table has two fields: the beverage name and its product code.
The “code” field will be used to perform the record matching.
Regular Beverages:
Name
Budweiser
Coca-Cola
Pepsi
Code
BUDWEISER
COCACOLA
PEPSI
Calorie-Free Beverages:
Code
COCACOLA
FRESCA
PEPSI
PEPSI
Water
Name
Diet Coca-Cola
Fresca
Diet Pepsi
Pepsi Light
Purified Water
Let’s join this table by the code field. Whereas the order of the joined tables makes sense in
some cases, we will consider the following statement:
[Beverage] JOIN [Calorie-Free Beverage]
i.e. [Beverage] is from the left of the join operator, and [Calorie-Free Beverage] is from the
right.
1. INNER JOIN: Result set will contain only those data where the criteria match. In our example
we will get 3 records: 1 with COCACOLA and 2 with PEPSI codes.
2. OUTER JOIN: OUTER JOIN will always contain the results of INNER JOIN, however it can
contain some records that have no matching record in other table. OUTER JOINs are divided
to following subtypes:
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