SQL WHERE Clause

SQL

SQL WHERE Clause : SQL WHERE Clause is used to filter records and to extract only those records that fulfill a specified condition.

  • The WHERE clause is used to filter records.
  • The WHERE clause is used to extract only those records that fulfill a specified condition.

WHERE Syntax

SELECT column1, column2, …
FROM table_name
WHERE condition;

Note: The WHERE clause is not only used in SELECT statement, it is also used in UPDATE, DELETE statement, etc.!

 

Demo Database

Below is a selection from the “Customers” table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

 

WHERE Clause Example

The following SQL statement selects all the customers from the country “Mexico”, in the “Customers” table:

Example

SELECT * FROM Customers
WHERE Country=’Mexico’;

 

Output

Number of Records: 5

CustomerID CustomerName ContactName Address City PostalCode Country
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
13 Centro comercial Moctezuma Francisco Chang Sierras de Granada 9993 México D.F. 05022 Mexico
58 Pericles Comidas clásicas Guillermo Fernández Calle Dr. Jorge Cash 321 México D.F. 05033 Mexico
80 Tortuga Restaurante Miguel Angel Paolino Avda. Azteca 123 México D.F. 05033 Mexico

 

 

Text Fields vs. Numeric Fields

SQL requires single quotes around text values (most database systems will also allow double quotes).

However, numeric fields should not be enclosed in quotes:

Example

SELECT * FROM Customers
WHERE CustomerID=1;

 

Output

Number of Records: 1

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany

 

Operators in The WHERE Clause

The following operators can be used in the WHERE clause:

Operator Description
= Equal
<> Not equal. Note: In some versions of SQL this operator may be written as !=
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
BETWEEN Between an inclusive range
LIKE Search for a pattern
IN To specify multiple possible values for a column