Question

I’m surprised that there isn’t already an answer for this… it suggests to me that I’m doing something fundamentally wrong. Or everyone else is.

Let’s say I have an array of possibly repeating values that were sorted client-side coming in as a POST request and the goal is to return a result-set from MySQL indexed by those values and in the same order as those values and preserving the redundancies!!!

So, if the values were: 1,2,3,2,3,4,5,5,5

The desired result is:

+----+-------+
| id | value |
+----+-------+
|  1 | one   |
|  2 | two   |
|  3 | three |
|  2 | two   |
|  3 | three |
|  4 | four  |
|  5 | five  |
|  5 | five  |
|  5 | five  |
+----+-------+

The code below seems to work, but Christ, seriously? I have to abuse array_intersect() and have two different loops, one of them nested, just to make a simple result set get ordered and repeated in the same pattern as the input array? This can’t be how it’s really supposed to be done.

function repQuery($inids,$incol,$querystring,$emptyval = "NULL"){
    # incol is the name of a column in the query
    # inids is an array within which the value of incol must be found
    # querystring is a query of the form...
    # "select FOO from BAR where %s in (%s) BLAH BLAH BLAH"
    # The first %s will be replaced by $incol and the second by $inids
    $qq = mysql_query(sprintf($querystring,$incol,implode(",",$inids))) or die(mysql_error());
    $nf = mysql_num_fields($qq); $dummyrow = array();
    for($ii = 0; $ii < $nf; $ii+= 1){
        $dummyrow[mysql_field_name($qq,$ii)] = $emptyval;
    };
    $out = array_fill(0,count($inids),$dummyrow);
    while($rr = mysql_fetch_assoc($qq)){
        foreach(array_keys(array_intersect($inids,array($rr[$incol]))) as $ii) {
            $out[(int)$ii] = $rr;
        }
    }
    return $out;
}

My question is: is there some accepted pattern or PHP array command or something else that I’m overlooking? In R the above would be a one-liner.

Answer 1

While it would be awesome if it were a feature in MySQL, I don’t think there is a way to use ORDER BY with a repeating pattern (you can get a “custom pattern” via ORDER BY FIELD(), but not quite there).

I’m not sure about any special methods in PHP just for this, but using a temporary array might be able to reduce the headache:

function repQuery($inids,$incol,$querystring,$emptyval = "NULL"){
    $qq = mysql_query(sprintf($querystring,$incol,implode(",",$inids))) or die(mysql_error());

    // build a temporary array of all of the results - the row's "ID" is the array index
    $tmpResults = array();
    while ($row = mysql_fetch_assoc($qq)) {
        $tmpResults[$row['id']] = $row;
    }

    // iterate through the order/list of IDs and insert each result one after the other
    $out = array();
    foreach ($inids as $id) {
        $out[] = $tmpResults[$id];
    }
    return $out;
}

This will place every SQL result (one for each ID) in the $tmpResults array using the row’s ID as the array’s index. The next step is to iterate through the $inids list, which contains the pattern to replicate, and to insert the corresponding record-result into the $out array.