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In the previous chapters, we were getting data from one table at a time. This is good enough for simple takes, but in most of the real world MySQL usages, you will often need to get data from multiple tables in a single query.

You can use multiple tables in your single SQL query. The act of joining in MySQL refers to smashing two or more tables into a single table.

You can use JOINS in the SELECT, UPDATE and DELETE statements to join the MySQL tables. We will see an example of the LEFT JOIN also which is different from the simple MySQL JOIN.

Using Joins in a PHP Script

You can use any of the above-mentioned SQL query in the PHP script. You only need to pass the SQL query into the PHP function mysqli_query() and then you will fetch results in the usual way.

Example

The following example −

<?php
   $dbhost = 'remotemysql.com:3036';
   $dbuser = 'your_username;
   $dbpass = 'your_password';
   $conn = mysqli_connect($dbhost, $dbuser, $dbpass);
   
   if(! $conn ) {
      die('Could not connect: ' . mysqli_error());
   }

   $sql = 'SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
      FROM tutorials_tbl a, tcount_tbl b
      WHERE a.tutorial_author = b.tutorial_author';

   mysqli_select_db('TUTORIALS');
   $retval = mysqli_query( $sql, $conn );

   if(! $retval ) {
      die('Could not get data: ' . mysqli_error());
   }

   while($row = mysqli_fetch_array($retval, mysqli_ASSOC)) {
      echo "Author:{$row['tutorial_author']}  <br> ".
         "Count: {$row['tutorial_count']} <br> ".
         "Tutorial ID: {$row['tutorial_id']} <br> ".
         "--------------------------------<br>";
   } 
   echo "Fetched data successfully\n";
   mysqli_close($conn);
?>

MySQL LEFT JOIN

A MySQL left join is different from a simple join. A MySQL LEFT JOIN gives some extra consideration to the table that is on the left.

If I do a LEFT JOIN, I get all the records that match in the same way and IN ADDITION I get an extra record for each unmatched record in the left table of the join: thus ensuring (in my example) that every AUTHOR gets a mention.

Example

Try the following example to understand the LEFT JOIN.

your_username@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
   -> FROM tutorials_tbl a LEFT JOIN tcount_tbl b
   -> ON a.tutorial_author = b.tutorial_author;
+-------------+-----------------+----------------+
| tutorial_id | tutorial_author | tutorial_count |
+-------------+-----------------+----------------+
|      1      |    John Poul    |       1        |
|      2      |     Abdul S     |      NULL      |
|      3      |     Sanjay      |       1        |
+-------------+-----------------+----------------+
3 rows in set (0.02 sec)

You would need to do more practice to become familiar with JOINS. This is slightly a bit complex concept in MySQL/SQL and will become more clear while doing real examples.

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