Check if two ranges intersect in a database with php - php

Question

I have a database that has 2 columns Left_From and Left_To I need to basically check both columns with each row in the database to see if there is any overlapping ranges. So lets say there are 37 rows returned I need to check each row 37 times. I have tried array_intersect() with ranges and multiple loops. I have also tried BETWEEN in mysql but that does do what I need it to either. When I tried the between method I have two loops that I thought would take these two
$newstart[$crow] = $row['LEFT_FROM'];
$newend[$crow] = $row['LEFT_TO'];
and compare them to the new data that would be looped through 37 times because of $row2.
//attempt at BETWEEN
$newstart = array();
$newend = array();
$crow = 0;
while ($row = mysqli_fetch_array($get)) {
$newstart[$crow] = $row['LEFT_FROM'];
$newend[$crow] = $row['LEFT_TO'];
while ($row2 = mysqli_fetch_array($get)) {
$newsql = "SELECT * FROM database+table WHERE tablename = 'something' AND
LEFT_FROM BETWEEN " . $newstart[$crow] . " AND " . $newend[$crow] . " OR
LEFT_TO BETWEEN " . $newstart[$crow] . " AND " . $newend[$crow] . " OR ".
$newstart[$crow] . " BETWEEN " . "LEFT_FROM" . " AND ". " LEFT_TO";
$result = mysqli_query($GLOBALS['Con'], $newsql);
if (!$result) {
echo "Error: " . mysqli_error($GLOBALS['Con']) . "<br>";
}
if (!empty($result)) {
echo "Overlap: ". "Row2 LEFT_FROM: " . $row2['LEFT_FROM'] . " NewStart: " . $newstart[$crow] . " Row2 LEFT_TO: " . $row2['LEFT_TO'] . " Newend: " . $newend[$crow] . "<br>" . "Crow: " . $crow . "<br>" ;
}
}
echo "Crow: " . $crow . "<br>";
$crow++;
}
atempt at array_intersect all variables in arrays are set to 0
$result = mysqli_query($GLOBALS['con'], $select);
$Rows = $result->num_rows;
$Rows2 = $Rows;
$Rows3 = $Rows;
$Rows4 = $Rows;
$Rows5 = $Rows;
$range1 = array();
$range2 = array();
$range3 = array();
$range4 = array();
while ($counter <= $Rows) {
$range1[$crow] = $leftfrom[$add];
$range2[$crow] = $leftto[$add];
$counter++;
$road++;
$crow++;
}
while ($counter2 <= $Rows2) {
$range3[$crow2] = $leftfrom[$add2];
$range4[$crow2] = $leftto[$add2];
$counter2++;
$road3++;
$crow2++;
}
$Combined1 = array();
$Combined1 = array();
while ($counter3 <= $Rows3) {
$Combined1[$crow5] = range($range1[$crow3], $range2[$crow3]);
$Combined2[$crow6] = range($range3[$crow3], $range4[$crow3]);
$crow5++;
$crow6++;
$crow3++;
$counter3++;
}
$check1 = 0;
while ($check1 <= $Rows4) {
$GLOBALS['check2'] = 0;
$Rows6 = $GLOBALS['check2'] + 1;
while ($GLOBALS['check2'] <= $Rows5) {
$results = array_intersect($Combined1[$check1],$Combined2[$Rows6]);
if ($results) {
$start = reset($results);
$end = end($results);
echo "These are overlapping" . "<br>";
echo "Start of overlap: " . $start . " Rows#: " . $check1 . " Bad Row: " . $GLOBALS['check2'];
echo "<br>";
echo "end of overlap: " . $end;
echo "<br>" . $GLOBALS['check2'] ;
$GLOBALS['check2']++;
}else{
echo "<br>" . $check1 . " No duplicates" . "<br>";
$GLOBALS['check2']++;
}
}
$check1++;
}

Answer 1

You don't need a loop in PHP, you can do it entirely by joining the table with itself.
SELECT *
FROM yourTable AS t1
JOIN yourTable AS t2
ON t1.id < t2.id
AND (t1.left_from <= t2.left_to AND t2.left_from <= t1.left_to)
t1.id < t2.id keeps it from treating a row as overlapping with itself (and using < rather than != keeps it from showing the same pair of rows twice). Replace id with the primary key of your table.

Answer 2

To check, if two number ranges overlap, you could use the simple test x1 < y2 AND y1 < x2. This could be combined in a single sql statement.
SELECT
t1.LEFT_FROM as LEFT_FROM_1,
t1.LEFT_TO as LEFT_TO_1,
t2.LEFT_FROM as LEFT_FROM_2,
t2.LEFT_TO as LEFT_TO_2
FROM
t t1, t t2
WHERE
t1.LEFT_FROM < t2.LEFT_TO AND t2.LEFT_FROM < t1.LEFT_TO
This query would return all overlapping ranges.