WHERE Clause
In this tutorial, we are going to discuss about the WHERE Clause in DQL. In Data Query Language (DQL), the WHERE
clause is used to filter records. It specifies conditions that must be met for records to be selected. The syntax for a WHERE
clause in DQL is similar to SQL and is used in a SELECT
statement to limit the results returned by the query.
![WHERE Clause](https://waytoeasylearn.com/storage/2024/07/DQL.jpg)
WHERE
In MySQL, the WHERE
clause is used to filter the rows returned by a SELECT
, UPDATE
, or DELETE
statement. It allows you to specify a condition that must be met for a row to be included in the result set.
Syntax
The basic syntax of a WHERE
clause in a SELECT
statement is as follows:
SELECT column1, column2, column3, ...
FROM table_name
WHERE condition;
Example
Suppose we have a table named Employees
with the following columns: EmployeeID
, FirstName
, LastName
, Department
, and Salary
. To select records where the Department
is ‘Sales’, you would use:
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE Department = 'Sales';
Common Operators in the WHERE Clause
=
: Equal<>
or!=
: Not equal>
: Greater than<
: Less than>=
: Greater than or equal<=
: Less than or equalBETWEEN
: Between an inclusive rangeLIKE
: Search for a patternIN
: Specify multiple possible values for a column
Combining Conditions
You can combine multiple conditions using logical operators such as AND
, OR
, and NOT
.
Example with AND
and OR
To select records where the Department
is ‘Sales’ and the Salary
is greater than 50000, you would use:
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE Department = 'Sales' AND Salary > 50000;
To select records where the Department
is either ‘Sales’ or ‘Marketing’, you would use:
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE Department = 'Sales' OR Department = 'Marketing';
Using LIKE for Pattern Matching
To select records where the LastName
starts with ‘venkat’, you would use:
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE LastName LIKE 'venkat%';
Using BETWEEN for Range
To select records where the Salary
is between 40000 and 60000, you would use:
SELECT EmployeeID, FirstName, LastName, Department, Salary
FROM Employees
WHERE Salary BETWEEN 40000 AND 60000;
The WHERE
clause is a powerful tool in DQL for filtering and refining the data you retrieve from a database.
That’s all about the WHERE Clause in DQL. If you have any queries or feedback, please write us at contact@waytoeasylearn.com. Enjoy learning, Enjoy SQL..!!