Detailed examples of the application of Join in Mysql
In this chapter we will introduce to you how to use MySQL's JOIN to query data in two or more tables. Friends who are interested in join in mysql should learn together
In the previous chapters, we have learned how to read data in a table. This is relatively simple, but it is often needed in real applications. Read data from multiple data tables.
In this chapter we will introduce to you how to use MySQL's JOIN to query data in two or more tables.
You can use Mysql's join in SELECT, UPDATE and DELETE statements to combine multiple table queries.
Below we will demonstrate the difference between the use of MySQL LEFT JOIN and JOIN.
Using JOIN in the command prompt
We have two tables tcount_tbl and runoob_tbl in the RUNOOB database. The data of the two data tables are as follows:
Example
Try the following example:
root@host# mysql -u root -p password; Enter password:******* mysql> use RUNOOB; Database changed mysql> SELECT * FROM tcount_tbl; +-----------------+----------------+ | runoob_author | runoob_count | +-----------------+----------------+ | mahran | 20 | | mahnaz | NULL | | Jen | NULL | | Gill | 20 | | John Poul | 1 | | Sanjay | 1 | +-----------------+----------------+ 6 rows in set (0.01 sec) mysql> SELECT * from runoob_tbl; +-------------+----------------+-----------------+-----------------+ | runoob_id | runoob_title | runoob_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 1 | Learn PHP | John Poul | 2007-05-24 | | 2 | Learn MySQL | Abdul S | 2007-05-24 | | 3 | JAVA Tutorial | Sanjay | 2007-05-06 | +-------------+----------------+-----------------+-----------------+ 3 rows in set (0.00 sec) mysql>
Next we will use MySQL's JOIN to connect the above two tables to read the runoob_tbl table The runoob_count field value corresponding to all runoob_author fields in the tcount_tbl table:
mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count -> FROM runoob_tbl a, tcount_tbl b -> WHERE a.runoob_author = b.runoob_author; +-------------+-----------------+----------------+ | runoob_id | runoob_author | runoob_count | +-------------+-----------------+----------------+ | 1 | John Poul | 1 | | 3 | Sanjay | 1 | +-------------+-----------------+----------------+ 2 rows in set (0.01 sec) mysql>
Use JOIN in PHP script
Use in PHP mysql_query()functionTo execute a SQL statement, you can use the same SQL statement above as the parameter of the mysql_query()function.
Try the following example:
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn )
{
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT a.runoob_id, a.runoob_author, b.runoob_count
FROM runoob_tbl a, tcount_tbl b
WHERE a.runoob_author = b.runoob_author';
mysql_select_db('RUNOOB');
$retval = mysql_query( $sql, $conn );
if(! $retval )
{
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC))
{
echo "Author:{$row['runoob_author']} <br> ".
"Count: {$row['runoob_count']} <br> ".
"Tutorial ID: {$row['runoob_id']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>MySQL LEFT JOIN
MySQL left join is different from join. MySQL LEFT JOIN will read all the data in the left data table, even if there is no corresponding data in the right table.
Example
Try the following example to understand the application of MySQL LEFT JOIN:
root@host# mysql -u root -p password; Enter password:******* mysql> use RUNOOB; Database changed mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count -> FROM runoob_tbl a LEFT JOIN tcount_tbl b -> ON a.runoob_author = b.runoob_author; +-------------+-----------------+----------------+ | runoob_id | runoob_author | runoob_count | +-------------+-----------------+----------------+ | 1 | John Poul | 1 | | 2 | Abdul S | NULL | | 3 | Sanjay | 1 | +-------------+-----------------+----------------+ 3 rows in set (0.02 sec)
LEFT JOIN is used in the above example. This statement will read the data table runoob_tbl on the left All selected field data, even if there is no corresponding runoob_author field value in the right table tcount_tbl.
The above is the detailed content of Detailed examples of the application of Join in Mysql. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
MySQL's Role: Databases in Web Applications
Apr 17, 2025 am 12:23 AM
The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.
How to start mysql by docker
Apr 15, 2025 pm 12:09 PM
The process of starting MySQL in Docker consists of the following steps: Pull the MySQL image to create and start the container, set the root user password, and map the port verification connection Create the database and the user grants all permissions to the database
Laravel Introduction Example
Apr 18, 2025 pm 12:45 PM
Laravel is a PHP framework for easy building of web applications. It provides a range of powerful features including: Installation: Install the Laravel CLI globally with Composer and create applications in the project directory. Routing: Define the relationship between the URL and the handler in routes/web.php. View: Create a view in resources/views to render the application's interface. Database Integration: Provides out-of-the-box integration with databases such as MySQL and uses migration to create and modify tables. Model and Controller: The model represents the database entity and the controller processes HTTP requests.
Solve database connection problem: a practical case of using minii/db library
Apr 18, 2025 am 07:09 AM
I encountered a tricky problem when developing a small application: the need to quickly integrate a lightweight database operation library. After trying multiple libraries, I found that they either have too much functionality or are not very compatible. Eventually, I found minii/db, a simplified version based on Yii2 that solved my problem perfectly.
How to install mysql in centos7
Apr 14, 2025 pm 08:30 PM
The key to installing MySQL elegantly is to add the official MySQL repository. The specific steps are as follows: Download the MySQL official GPG key to prevent phishing attacks. Add MySQL repository file: rpm -Uvh https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm Update yum repository cache: yum update installation MySQL: yum install mysql-server startup MySQL service: systemctl start mysqld set up booting
Centos install mysql
Apr 14, 2025 pm 08:09 PM
Installing MySQL on CentOS involves the following steps: Adding the appropriate MySQL yum source. Execute the yum install mysql-server command to install the MySQL server. Use the mysql_secure_installation command to make security settings, such as setting the root user password. Customize the MySQL configuration file as needed. Tune MySQL parameters and optimize databases for performance.
Laravel framework installation method
Apr 18, 2025 pm 12:54 PM
Article summary: This article provides detailed step-by-step instructions to guide readers on how to easily install the Laravel framework. Laravel is a powerful PHP framework that speeds up the development process of web applications. This tutorial covers the installation process from system requirements to configuring databases and setting up routing. By following these steps, readers can quickly and efficiently lay a solid foundation for their Laravel project.
MySQL vs. Other Programming Languages: A Comparison
Apr 19, 2025 am 12:22 AM
Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.
