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SQL is a standard language for storing, manipulating and retrieving data in databases.

Our SQL tutorial will teach you how to use SQL in: MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, Postgres, and other database systems.

Start learning SQL now »

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Examples in Each Chapter

With our online SQL editor, you can edit the SQL statements, and click on a button to view the result.

Click on the "Try it Yourself" button to see how it works.

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SQL Exercises

Test Yourself With Exercises

Exercise:

Insert the missing statement to get all the columns from the Customers table.

Start the Exercise

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SQL Examples

Learn by examples! This tutorial supplements all explanations with clarifying examples.

See All SQL Examples

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SQL Quiz Test

Test your SQL skills at W3Schools!

Start SQL Quiz!

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My Learning

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Log into your account, and start earning points!

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SQL References

At W3Schools you will find a complete reference for keywords and function:

SQL Keyword Reference

MYSQL Functions

SQLServer Functions

MS Access Functions

SQL Quick Reference

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SQL Data Types

Data types and ranges for Microsoft Access, MySQL and SQL Server.

SQL Data Types

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MySQL is a widely used relational database management system (RDBMS).

MySQL is free and open-source.

MySQL is ideal for both small and large applications.

Start learning MySQL now »

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Examples in Each Chapter

With our online MySQL editor, you can edit the SQL statements, and click on a button to view the result.

Click on the "Try it Yourself" button to see how it works.

---

MySQL Exercises

Test Yourself With Exercises

Exercise:

Insert the missing statement to get all the columns from the Customers table.

Start the Exercise

---

---

MySQL Examples

Learn by examples! This tutorial supplements all explanations with clarifying examples.

See All SQL Examples

---

MySQL Quiz Test

Test your MySQL skills at W3Schools!

Start MySQL Quiz!

---

My Learning

Track your progress with the free "My Learning" program here at W3Schools.

Log into your account, and start earning points!

This is an optional feature, you can study W3Schools without using My Learning.

---

MySQL References

At W3Schools you will find a complete reference of MySQL data types and functions:

MySQL Data Types

MySQL Functions

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AJAX can be used for interactive communication with a database.

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AJAX Database Example

The following example will demonstrate how a web page can fetch information from a database with AJAX:

Example

Person info will be listed here...

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Example Explained - The MySQL Database

The database table we use in the example above looks like this:

id	FirstName	LastName	Age	Hometown	Job
1	Peter	Griffin	41	Quahog	Brewery
2	Lois	Griffin	40	Newport	Piano Teacher
3	Joseph	Swanson	39	Quahog	Police Officer
4	Glenn	Quagmire	41	Quahog	Pilot

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Example Explained

In the example above, when a user selects a person in the dropdown list above, a function called "showUser()" is executed.

The function is triggered by the onchange event.

Here is the HTML code:

Example

  Select a person:
  Peter Griffin
  Lois Griffin
  Joseph Swanson
  Glenn Quagmire
 

Run example »

Code explanation:

First, check if person is selected. If no person is selected (str == ""), clear the content of txtHint and exit the function. If a person is selected, do the following:

• Create an XMLHttpRequest object
• Create the function to be executed when the server response is ready
• Send the request off to a file on the server
• Notice that a parameter (q) is added to the URL (with the content of the dropdown list)

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The PHP File

The page on the server called by the JavaScript above is a PHP file called "getuser.php".

The source code in "getuser.php" runs a query against a MySQL database, and returns the result in an HTML table:

$q = intval($_GET['q']);

$con = mysqli_connect('localhost','peter','abc123');
if (!$con) {
  die('Could not connect: ' . mysqli_error($con));
}

mysqli_select_db($con,"ajax_demo");
$sql="SELECT * FROM user WHERE id = '".$q."'";
$result = mysqli_query($con,$sql);

echo "

";
while($row = mysqli_fetch_array($result)) {
  echo "";
  echo "";
  echo "";
  echo "";
  echo "";
  echo "";
  echo "";
}
echo "

Firstname	Lastname	Age	Hometown	Job
" . $row['FirstName'] . "	" . $row['LastName'] . "	" . $row['Age'] . "	" . $row['Hometown'] . "	" . $row['Job'] . "

";
mysqli_close($con);
?>

Explanation: When the query is sent from the JavaScript to the PHP file, the following happens:

1. PHP opens a connection to a MySQL server
2. The correct person is found
3. An HTML table is created, filled with data, and sent back to the "txtHint" placeholder