How to fetch from 3 tables? - php

Question

I'm building a job search site and I have 3 tables.
1: jobs_table: id, user_id, job_title, location, job_description, currency, salary, salary_type, employment_type, post_time, visiblity
2: applications_table: id, creator_id, applicant_id, job_id, status
3: user_table: id, profile_picture, first_name, last_name, phone_number, email_address, password, data, verification_key, modify_date
Currently, I'm selecting from the jobs_table based on user input (PHP code below), however, I'm trying to also display to the user which jobs they have already applied for and to do this I need to select from the Jobs_table (get the jobs data as I'm already doing), but also select from the applications_table with the current users ID to check if there is a row with the applicant_id and job_id if this row exists then the user has already applied for that position.
Any help is much appreciated.
PHP
$conditions = [];
// Start by processing the user input into a data structure that can be used to construct the query
if (!empty($t)) {
$conditions[] = [
['job_title', 'LIKE', '%' . $t . '%'],
];
}
if (!empty($l)) {
$conditions[] = [
['location', '=', $l],
];
}
if (!empty($s)) {
$conditions[] = [
['salary', '>=', $s],
];
}
// Loop the conditions and process them into valid SQL strings
$bindValues = [];
$whereClauseParts = [];
foreach ($conditions as $conditionSet) {
$set = [];
foreach ($conditionSet as $condition) {
list($fieldName, $operator, $value) = $condition;
$set[] = "`{$fieldName}` {$operator} :{$fieldName}";
$bindValues[$fieldName] = $value;
}
$whereClauseParts[] = implode(' OR ', $set);
}
$statement = "SELECT * FROM 001_jobs_table_as WHERE visiblity = 2";
if (!empty($whereClauseParts)) {
$statement .= " AND (" . implode(') AND (', $whereClauseParts) . ")";
}
/* Pagination Code starts */
$per_page_html = '';
$page = 1;
$start=0;
if(!empty($_GET["page"])) {
$page = $_GET["page"];
$start=($page-1) * ROW_PER_PAGE;
}
$limit=" limit " . $start . "," . ROW_PER_PAGE;
$pagination_statement = $dbh->prepare($statement);
$pagination_statement->execute($bindValues);
$row_count = $pagination_statement->rowCount();
if(!empty($row_count)){
$per_page_html .= "<div class='page_row_selector'>";
$page_count=ceil($row_count/ROW_PER_PAGE);
if($page_count>1) {
for($i=1;$i<=$page_count;$i++){
if($i==$page){
$per_page_html .= '<input type="submit" name="page" value="' . $i . '" class="btn-page active_page" />';
} else {
$per_page_html .= '<input type="submit" name="page" value="' . $i . '" class="btn-page" />';
}
}
}
$per_page_html .= "</div>";
}
$query = $statement.$limit;
$pdo_statement = $dbh->prepare($query);
$pdo_statement->execute($bindValues);
$result = $pdo_statement->fetchAll();
if(empty($result)) { ?>
<div class="job_card">
<h1 class="display-5 text-center no_result_message"> No match found. </h1>
</div>
<?php }else{
foreach($result as $row) {
$user_id = $row['user_id'];
$job_key = $row['id'];
$job_title = $row['job_title'];
$location = $row['location'];
$job_description = $row['job_description'];
$employment_type = $row['employment_type'];
$salary = $row['salary'];
$salary_type = $row['salary_type'];
$currency = $row['currency'];
$post_time = $row['post_time'];
$user_id = $row['user_id'];
$to_time = time();
$from_time = strtotime($post_time);
$time_elapsed = $to_time - $from_time;
$seconds = round(abs($time_elapsed));
$minutes = round(abs($time_elapsed) / 60);
$hours = round(abs($time_elapsed) / 3600);
$days = round(abs($time_elapsed) / 86400);
$weeks = round(abs($time_elapsed) / 604800);
// display job information in here.
} ?>
UPDATE:
I have now revised my SELECT query to the following:
$statement = "SELECT * FROM 001_jobs_table_as jt";
$statement .= " LEFT JOIN 001_application_table_as at ON at.job_id = jt.jt_id";
$statement .= " RIGHT JOIN 001_user_table_as ut ON ut.id = at.applicant_id";
$statement .= " WHERE jt.visiblity = 2";
However, I'm getting duplicates in the results, every user that applies for a job duplicates that job in the results.

Answer 1

What about using LEFT JOIN?
The LEFT JOIN keyword returns all records from the left table
(table1), and the matched records from the right table (table2).
SELECT *, id AS jt_id FROM jobs_table jt
LEFT JOIN applications_table at ON jt.jt_id = at.job_id AND jt.user_id = at.applicant_id
WHERE jt.visibility = 2 AND (jt.job_title LIKE :job_title) AND (jt.location = :location) AND (jt.salary >= :salary);
This should return all rows from jobs_table which match searched criteria and some of those rows can have extra data from applications_table if user already applied to that specific job (row) from jobs_table.
Something like:
jt_id user_id job_title location ... id applicant_id job_id
=================================================================
1 15 php dev london
2 23 java dev liverpool
3 44 haskell manchester
4 52 front end bristol 7 52 4
5 66 golang leeds
Row with jt_id = 4 has some extra values meaning user already applied to that job.
This should give you some directions but unfortunatelly, i didn't have a time to test this query.
EDIT
I've made a mistake. LEFT JOIN should go before WHERE clause...silly me. Check the query once again, it has been updated.
Or try it online