SQL WHERE Clause

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The SQL WHERE Clause

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

If you want to select a subset of rows from a table, you use the WHERE clause in your SELECT statement.

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Below is a selection from the Customers table used in the examples:

Customers Table:

CustomerID	CustomerName	City	Country
1	Alfreds Futterkiste	Berlin	Germany
2	Ana Trujillo Emparedados	México D.F.	Mexico
3	Antonio Moreno Taquería	México D.F.	Mexico
4	Around the Horn	London	UK

The following SQL statement selects all customers from the country "Mexico".

SELECT * FROM Customers
WHERE Country = 'Mexico';

-- This query would return all customers where the country is Mexico.
SELECT * FROM Customers
WHERE Country = 'Mexico';

The result set would be:

CustomerID	CustomerName	City	Country
2	Ana Trujillo Emparedados	México D.F.	Mexico
3	Antonio Moreno Taquería	México D.F.	Mexico

Note: SQL uses single quotes for text values (most database systems will also accept double quotes).

The following SQL statement selects all customers with a CustomerID greater than 2.

SELECT * FROM Customers
WHERE CustomerID > 2;

Numeric values should not be enclosed in quotes.

You can use various operators in the WHERE clause to build your conditions.

Operator	Description
`=`	Equal
`>`	Greater than
`<`	Less than
`>=`	Greater than or equal
`<=`	Less than or equal
`<>` or `!=`	Not equal
`BETWEEN`	Between a certain range
`LIKE`	Search for a pattern
`IN`	To specify multiple possible values for a column

We will cover these operators in more detail in the upcoming chapters.

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