SQL WHERE Clause

The WHERE clause is used to extract only those records that fulfill a specified criterion.

SQL WHERE Syntax :
-------------------
SELECT column_name(s)
FROM table_name
WHERE column_name operator value

WHERE Clause Example
---------------------
The "Persons" table:

P_Id LastName FirstName Address City
------------------------------------
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

Now we want to select only the persons living in the city "Sandnes" from the table above.

We use the following SELECT statement:
-------------------------------------
SELECT * FROM Persons
WHERE City='Sandnes'

The result-set will look like this:
-------------------------------------
P_Id LastName FirstName Address City
-------------------------------------
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes

Quotes Around Text Fields:
----------------------------
SQL uses single quotes around text values (most database systems will also accept double quotes).

Although, numeric values should not be enclosed in quotes.

For text values:
------------------

This is correct:

SELECT * FROM Persons WHERE FirstName='Tove'

This is wrong:

SELECT * FROM Persons WHERE FirstName=Tove

For numeric values:
--------------------

This is correct:

SELECT * FROM Persons WHERE Year=1965

This is wrong:

SELECT * FROM Persons WHERE Year='1965'

Operators Allowed in the WHERE Clause
-------------------------------------
With the WHERE clause, the following operators can be used:

Operator Description
= Equal
<> Not equal
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
BETWEEN Between an inclusive range
LIKE Search for a pattern
IN If you know the exact value you want to return for at least one of the columns

"Note: In some versions of SQL the <> operator may be written as !="