Implementing FULL Join in MySQL

In the previous articles we saw what inner joins, left joins and right joins are and how they are used. Full joins are simplest of all the joins. Full join retrieves all the records from both the right and left tables irrespective of the similar values in the common column. Consider the example of patient and department table. The Full join will retrieve all the patient records and all the department records, if patient doesnt have a corresponding department, the fields for department columns will remain empty. Vice versa will be the case for department, records. An important point to note here is that unlike MS SQLSERVER and some of the other databases, MySQL doesnt support FULL JOIN directly. Rather, we take right join and left join and then take union of both.

This might sound complex at first. Lets again have a look at our patient and department table.

Patient Table

 

patient_id	patient_fname	patient_lname	patient_age	dep_id
1	Mike	Getting	20	3
2	Sara	Taylor	25	2
3	Vince	James	52	9
4	Shawn	Been	45	6
5	Lara	Bran	43	7
6	Fred	Vicks	8	5
7	Pam	Beesly	38	8

 

Department Table

 

dep_id	dep_name	dep_capacity
2	Neurology	200
3	Cardiology	300
4	Nephrology	200
5	Children	100
6	Pythology	400
7	Optician	500

 

Let’s implement full join on above two tables and see what result do we get. Have a look at the following examples.

 

   







connect_error) {
    die("Connection not established: " . $connection->connect_error);
} 
    
$query = "Use Hospital;";
$connection->query($query);
    
// Implementing RIGHT JOIN

$query = "SELECT patient.patient_fname, patient.patient_age, department.dep_name ".
    "FROM patient LEFT JOIN department ".
    "ON patient.dep_id = department.dep_id ".
    "UNION ".
    "SELECT patient.patient_fname, patient.patient_age, department.dep_name ".
    "FROM patient RIGHT JOIN department ".
    "ON patient.dep_id = department.dep_id ";
     
$output = $connection->query($query);

if ($output->num_rows > 0) {
    // output data of each row
    while($row = $output->fetch_assoc()) {
        echo "First Name: " . $row["patient_fname"]. " - Age: " . $row["patient_age"]. " - Department: " . $row["dep_name"]. "
";
    }
} else {
    echo "0 results";
}

$connection->close();
?>  
    

Download the code

The output of the above code will look like this.

First Name: Mike – Age: 20 – Department: Cardiology
First Name: Sara – Age: 25 – Department: Neurology
First Name: Vince – Age: 52 – Department:
First Name: Shawn – Age: 45 – Department: Pythology
First Name: Lara – Age: 43 – Department: Optician
First Name: Fred – Age: 8 – Department: Children
First Name: Pam – Age: 38 – Department:
First Name: – Age: – Department: Nephrology

It can be seen that all the records have been retrieved from both the patient and department tables and the fields have been left empty where there isnt any record found in the corresponding tables.

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