SQL Tutorial
SQL Where
The SQL WHERE Clause
Records can be filtered using the WHERE clause.
Its purpose is to extract records only when they meet a predetermined requirement.
Example
Select all customers from Mexico:
SELECT * FROM Customers
WHERE Country='Mexico';
Syntax
SELECT column1, column2, …
FROM table_name
WHERE condition;
Note: The WHERE clause is utilized in UPDATE, DELETE, and other SQL statements in addition to SELECT queries!
Demo 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 |
Text Fields vs. Numeric Fields
Text values in SQL must be surrounded by single quotes (double quotes are generally accepted as well).
Numerical fields, however, shouldn’t be surrounded by quotes:
Example
SELECT * FROM Customers
WHERE CustomerID=1;
Operators in The WHERE Clause
The = operator is not the only operator you may use to narrow down the search.
Example
Select all customers with a CustomerID greater than 80:
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 |
