mysql get first and last entry with same value in other column

Question

I have a table with a date column and a price column. The date column has a row for each day of the year.

The table is like this:

2017-09-01 158.00
2017-09-02 158.00
2017-09-03 158.00
2017-09-04 158.00
etc.
2017-09-10 175.00
2017-09-11 175.00
etc.
2017-10-20 158.00
2017-10-21 158.00

I want to get the first date and last date in a time range that has same price.

So the result for above should be:

    2017-09-01 -- 2017-09-04 158 euro.
    2017-09-10 -- 2017-09-11 175 euro.
    2017-10-20 -- 2017-10-21 158 euro.

Answer 1

See if this works for you. It's based on another answer I gave here. You loop through the days, accumulating every day that has the same price as before in an array. Every time the loop detects a change in the price, a new array is created, and so on.

<?php
$values[] = ["2017-09-01", "158.00"];
$values[] = ["2017-09-02", "158.00"];
$values[] = ["2017-09-03", "158.00"];
$values[] = ["2017-09-04", "158.00"];
$values[] = ["2017-09-10", "175.00"];
$values[] = ["2017-09-11", "175.00"];
$values[] = ["2017-10-20", "158.00"];
$values[] = ["2017-10-21", "158.00"];
$values[] = ["2017-10-22", "159.00"];
$values[] = ["2017-10-23", "152.00"];
$values[] = ["2017-10-24", "152.00"];
$ult = null;
$currentRange = [];
$ranges = [];
foreach ($values as $fecha) {
    $day = $fecha[0];
    $price = $fecha[1];
    if ($ult === null) {
        $currentRange = [
            "price" => $price, 
            "days" => [$day]
        ];
    }
    else {
        if ($price === $ult) {
            $currentRange["days"][] = $day;
        }
        else {
            $ranges[] = $currentRange;
            $currentRange = [
                "price" => $price, 
                "days" => [$day]
            ];
        }
    }
    $ult = $price;
}
$ranges[] = $currentRange;
$rangesString = [];
foreach ($ranges as $range) {
    $str = $range["days"][0];
    if (count($range["days"]) > 1) {
        $str .= " - ".$range["days"][count($range["days"]) - 1];
    }
    $str .= ": ".$range["price"];
    $rangesString[] = $str;
}
echo (implode("<br>", $rangesString));

/* results:
2017-09-01 - 2017-09-04: 158.00
2017-09-10 - 2017-09-11: 175.00
2017-10-20 - 2017-10-21: 158.00
2017-10-22: 159.00
2017-10-23 - 2017-10-24: 152.00
*/

Demo

Answer 2

If your date column is Dte and amount column is amt then your query should be like this

SELECT MIN(Dte), MAX(Dte), CONCAT(amt,' euro') FROM test 
GROUP BY amt