SQL Tutorial - WHERE Clause

In SQL SELECT, a WHERE clause can be used to specify conditions to filter the table further. We can filter an SQL Table based on a single column or more than one column. Imagine we have table called CUSTOMERS, with the following data:

Rambo

Robert

Belgium

Mugambo

Satraj

Norway

Nagashekar

Rao

India

Tom

Harry

Brazil

Dana

Laura

Australia

Rambo

Fox

New Zealand

Giselle

Chivvi

Japan

Scenario 1: Get me all records where Customer's First name is Rambo. We can use a WHERE Clause to specify the above criteria.

SELECT * from Customer WHERE FIRSTNAME = 'Rambo'

Result:

Rambo

Robert

Belgium

Rambo

Fox

New Zealand

In the above WHERE Clause, we used FIRSTNAME = 'Rambo'. It only fetches the records where FIRSTNAME equals Rambo.
We can use the Following operators in WHERE clause.

Operator	Meaning
=	Direct Equals Check
!= and <>	Not Equals Check
<	Columns Values that are less than the Right Hand Side value
<=	Column Values that are less than or equal to the Right Hand Side value
>	Column Values that are greater than the Right Hand Side value
>=	Column Values that are greater than or equal to the Right Hand Side value
IN	Gets ROWS where value is in the given set of values
NOT IN	Gets ROWS where value is not in the given set of values
BETWEEN	Gets ROWS where value is in between the given range
NOT BETWEEN	Gets ROWS where value is not in between the given set of values

Scenario 2: Get me all records where Customer's First name is Rambo, and Country is Belgium. We can combine two conditions with AND clause to achieve the above scenario.

SELECT * from Customer WHERE FIRSTNAME = 'Rambo' AND COUNTRY='Belgium'

Result:

Rambo

Robert

Belgium

In the above WHERE Clause, we used FIRSTNAME = "Rambo" and COUNTRY="Belgium". It only fetched the record where FIRSTNAME equals Rambo and COUNTRY equals Belgium.

Scenario 3: Get me all records where Customer's First name is Rambo or Mugambo. We can combine two conditions with OR clause to achieve the above scenario.

SELECT * from Customer WHERE FIRSTNAME = 'Rambo' OR FIRSTNAME='Mugambo'

Result:

Rambo

Robert

Belgium

Mugambo

Satraj

Norway

Rambo

Fox

New Zealand

In the above WHERE Clause, we used FIRSTNAME = 'Rambo' or FIRSTNAME='Mugambo'. It only fetched the record where FIRSTNAME equals Rambo or Mugambo.

Scenario 4: Get me all records where Customer's Age is below 30. We can use the less than < operator on Age column for the above scenario.

SELECT * from Customer WHERE AGE < 30

Result:

Rambo

Robert

Belgium

Tom

Harry

Brazil

Dana

Laura

Australia

In the above WHERE Clause, we used AGE < 30 in the WHERE clause to filter out rows based on Age.