Mysql select from two tables join - php

Question

i have two tables "employees" and "dependents",
Employees
|employee_No| Employee_name |
|1558 | Bean |
|1557 | Juliet |
|1556 | Zeke |
Dependents
|employee_No| dependent_name | relationship|
|1558 | Kelvin | Son |
|1558 | Mary | Daughter |
|1556 | Janet | Spouse |
is there a way i could get this data in one MySQL statement and display using php i.e. loop employees and dependent under that employee then move to the next employee.
current php code is
$employees = select_all_employees()
foreach ($employees as $covered){
echo $covered['Employee_name'].'<br/>';
$get_dependent = $select_dependent($covered["employee_No "]);
if($get_dependent != 0){
foreach($get_dependent as $details){
echo $details['dependent_name '].' '.$details['relationship'].'<br/>';
}
}
}
this takes too much time to load when there are thousand employees and dependents
expected outcome
|employee_No| dependent_name | relationship|
--------------------------------------------
|1558 | Bean | principal |
|1558 | Kelvin | Son |
|1558 | Mary | Daughter |
|1557 | Juliet | principal |
|1556 | Zeke | principal |
|1556 | Janet | Spouse |

Answer 1

The easiest way to get the results you want is with a UNION of the rows of the Employees table with the JOIN of the Employees with their Dependents. We do this UNION as a derived table so that we can then order the results by employee_No and also place the principal first for each employee_No. By doing it this way your PHP code becomes a simple loop over all the results.
SELECT employee_No, Employee_name AS dependent_name, 'principal' AS relationship
FROM Employees
UNION ALL
SELECT e.employee_No, d.dependent_name, d.relationship
FROM Employees e
JOIN Dependents d on d.employee_No = e.employee_No
ORDER BY employee_No DESC, relationship = 'principal' DESC
Output:
employee_No dependent_name relationship
1558 Bean principal
1558 Mary Daughter
1558 Kelvin Son
1557 Juliet principal
1556 Zeke principal
1556 Janet Spouse
Demo on dbfiddle

Answer 2

How about this query:
SELECT a.*, "principal" as 'relationship' FROM Employees a
UNION SELECT b.* FROM Dependents b ORDER BY employee_no DESC
DBFIDDLE here

Answer 3

You can use join or Map the columns. Check the index in both the tables for your slowness of query. Index should be employee_No in both the tables. And then loop your query output.
<?php
$qryOutput = array();
$query = "SELECT A.*, B.* FROM Employees A LEFT JOIN Dependents B ON A.employee_No=B.employee_No" // query
$qryOutput = execute_Query($query); // Check this syntax. For Execute query
// Loop through your Query Output
foreach ($qryOutput as $key => $value)
{ echo $value["employee_No"]." ".$value["dependent_name"]." ".$value["relationship"]; }
?>

Answer 4

You can use either INNER JOIN or LEFT JOIN to actualize it.
Try something like this. Though I have not tested the code.
Your table need to be created with foreign key references for it to work. see sample below. I have tested it.
create table Employees(employee_No int primary key,Employee_name varchar(100));
create table Dependents(employee_No int primary key,dependent_name varchar(100), relationship varchar(100)
foreign key (employee_No) references Employees(employee_No));
Insert for testing
insert into Employees(employee_No,Employee_name) values(1558,'Bean');
insert into Employees(employee_No,Employee_name) values(1557,'Juliet');
insert into Dependents(employee_No,dependent_name,relationship) values(1558,'kevin','son');
code
<?php
$host = "localhost"; /* Host name */
$user = "root"; /* User */
$password = ""; /* Password */
$dbname = "your-db"; /* Database name */
$con = mysqli_connect($host, $user, $password,$dbname);
// Check connection
if (!$con) {
die("Connection failed: " . mysqli_connect_error());
}
$query = 'SELECT Employees.employee_No, Employees.Employee_name, Dependents.employee_No, Dependents.dependent_name,
Dependents.relationship FROM Employees
LEFT JOIN Dependents ON Employees.employee_No = Dependents.employee_No
ORDER BY Employees.Employee_name';
$result = mysqli_query($con,$query);
while($row = mysqli_fetch_assoc($result)){
$empno = $row['employee_No'];
$empname = $row['Employee_name'];
$relation = $row['relationship'];
$dependant_name = $row['dependent_name'];
//you can now echo
echo $dependant_name.' '.$relation.'<br/>';
}
?>