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The WHERE clause is used to filter records
The WHERE
clause is used to filter records.
It 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
statements, it is also used in UPDATE
,
DELETE
, etc.!
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 |
The following SQL statement selects all the customers from the country "Mexico", in the "Customers" table:
SELECT * FROM Customers
WHERE Country='Mexico';
SQL requires single quotes around text values (most database systems will also allow double quotes).
However, numeric fields should not be enclosed in quotes:
SELECT * FROM Customers
WHERE CustomerID=1;
The following operators can be used in the WHERE
clause:
Operator | Description | Example |
---|---|---|
= | Equal | Try it |
> | Greater than | Try it |
< | Less than | Try it |
>= | Greater than or equal | Try it |
<= | Less than or equal | Try it |
<> | Not equal. Note: In some versions of SQL this operator may be written as != | Try it |
BETWEEN | Between a certain range | Try it |
LIKE | Search for a pattern | Try it |
IN | To specify multiple possible values for a column | Try it |
Select all records where the City
column has the value "Berlin".
SELECT * FROM Customers = ;