SQL Where Clause

The WHERE clause is used to specify a selection criteria.

The WHERE Clause 

To conditionally select data from a table, a WHERE clause can be added to the SELECT statement with the following syntax:

SELECT column FROM table WHERE column condition value

With the WHERE clause, these conditions can be used:

Operator	Condition
=	Equal
<>	Not equal
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal
BETWEEN	Between an inclusive range
LIKE	Explained below

Note: In some versions of SQL the not equal operator <> can be written as !=

Example: Select Persons from a City

To select only the people that live in Sandnes, add a WHERE clause to the SELECT statement like this: 

SELECT * FROM Persons WHERE City='Sandnes'

The "Persons" Table:

LastName	FirstName	Address	City	Year
Hansen	Ola	Timoteivn 10	Sandnes	1951
Svendson	Tove	Borgvn 23	Sandnes	1978
Svendson	Ståle	Kaivn 18	Sandnes	1980
Pettersen	Kari	Storgt 20	Stavanger	1960

The Result:

LastName	FirstName	Address	City	Year
Hansen	Ola	Timoteivn 10	Sandnes	1951
Svendson	Tove	Borgvn 23	Sandnes	1978
Svendson	Ståle	Kaivn 18	Sandnes	1980

Using Quotes

Note that we have used single quotes around the conditional values in the examples. SQL uses single quotes around text values. Most database systems will also accept double quotes. Numeric values should not be enclosed in quotes.

For Text values:

This is correct: SELECT * FROM Persons WHERE FirstName='Tove' This is not correct: SELECT * FROM Persons WHERE FirstName=Tove

For Numeric values:

This is correct: SELECT * FROM Persons WHERE Year>1965 This is not correct: SELECT * FROM Persons WHERE Year>'1965'

The LIKE Condition

The LIKE condition is used to specify a search for a pattern in a column.

The syntax is like this:

SELECT column FROM table WHERE column LIKE pattern

A "%" sign can be used to define wildcards (missing letters in the pattern) both before and after the pattern.

Example: Select Persons with a Name Pattern 

This SQL statement will return persons with a first name that start with an 'O'.

SELECT * FROM Persons WHERE FirstName LIKE 'O%'

This SQL statement will return persons with a first name that end with an 'a'.

SELECT * FROM Persons WHERE FirstName LIKE '%a'

This SQL statement will return persons with a first name that contains the pattern 'la'.

SELECT * FROM Persons WHERE FirstName LIKE '%la%'

All the examples above will return the following result:

LastName	FirstName	Address	City	Year
Hansen	Ola	Timoteivn 10	Sandnes	1951