Structured Query Language tutorial( where clause )

Structured Query Language tutorial( 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