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Sunday, 3 November 2013


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:


Id
LastName
FirstName
Address
City
1
Navis
Anto
Madras
TVL
2
ji
Bala
Bombay
TVL
3
Christopher
Franklin
America
KK

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

We use the following SELECT statement:

SELECT * FROM Persons
WHERE City='TVL'

The result-set will look like this:

Id
LastName
FirstName
Address
City
1
Navis
Anto
Madras
TVL
2
Ji
Bala
Bombay
TVL

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='Bala'

This is wrong:

SELECT * FROM Persons WHERE FirstName=Bala

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 !=

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