How To Use SQL LEFT JOIN Query With Example In PHP

Posted By Bajarangi soft , Posted On 18-09-2020

LEFT JOIN returns all records from the left table , and the matched records from the right table . if there is no match it will return NULL from right side table.

Syntax for SQL LEFT JOIN

SQL LEFT JOIN Syntax
SELECT column_name list
FROM table1
LEFT JOIN table2 ON table1.column_name=table2.column_name;

or:

SELECT column_name list
FROM table1
LEFT OUTER JOIN table2 ON table1.column_name=table2.column_name;

Lets Learn.
1.Create database and two tables
Course table.(left table)

CourseID	CourseName	CourseCode
1	Mechanical	ME20
2	Chemical	C20
3	Civil	CL20
4	Electrical	E20
5	Computer	CS20
6	Information	IS20
7	Electrical Electronics	EE20
8	Electrical Communication	ECE20

Student table.(right table)

StudentID	StudentName	Address	Section	Branch	Percentage	CourseID
1	Liam	23 Andrew road	A	CSE	66	5
2	Andrew	2415 Anthony market str	A	ISE	80	5
5	Charles	878 Eli Berguvsvägen 8	C	ECE	52	9
9	Andrew	2415 Anthony market str	A	CE	80	2
10	Bhavya	18 Christopher sq.	B	CE	67	9
12	Rajesh	878 Eli Berguvsvägen 8	C	CL	52	3
13	Daniel	878 Eli Berguvsvägen 8	ME	CSE	52	8
15	Connor	878 Eli Berguvsvägen 8	C	ME	52	1
16	Kiran	878 Eli Berguvsvägen 8	ME	ECE	52	10

Now we do SQL LEFT JOIN for both the table.

Example(1)

SELECT  course.CourseName ,student.StudentID
FROM course
LEFT JOIN student ON course.CourseID = student.StudentID
ORDER BY course.CourseName;

in this above example from "course" table selecting CourseName and from "student" table selecting StudentID from left course table joing right student table if there is courseid in student table which is in course table than it will fetch data or else it will return NULL.

2.Complete code of SQL LEFT JOIN in PHP script.

<!DOCTYPE html>
<html lang="en">
<head>
    <title>SQL LEFT JOIN </title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
</head>
<body>
<div class="container">
    <div class="text-center">
        <h1>SQL LEFT JOIN</h1>
    </div>
    <div class="well">
        <?php
        $connect = mysqli_connect("localhost", "root", "", "school_management");

        if ($connect->connect_error) {
            die("Connection failed: " . $connect->connect_error);
        }

        $sql_1 = "SELECT  course.CourseName ,student.StudentID
                  FROM course
                  LEFT JOIN student ON course.CourseID = student.StudentID
                  ORDER BY course.CourseName;";

        echo "<h2 class='text-danger'>SQL LEFT JOIN</h2>";
        if($result_1 = mysqli_query($connect, $sql_1)){
            if(mysqli_num_rows($result_1) > 0){
                echo "<table class='table'>
                    <tr>
                     <th>StudentID</th>
                    <th>CourseName</th>
                    </tr>
                    ";
                while($row = $result_1->fetch_assoc()){
                    echo "<tr>
                   <td>".$row['StudentID'] /*student table*/ ."</td>      
                   <td>".$row['CourseName'] /*student table*/ ."</td>      
                  </tr>";
                }
                echo "</table>";
            } else{
                echo "No records found.";
            }
        }
        ?>
    </div>
    <br>
</div>
</body>
</html>

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