Lookup a column value in recordset based on the value of another column

Question

I have a MySQL SELECT query (using wpdb_custom->get_results()) that returns two UNSIGNED TINYINT columns Col_1 and Col_2 for an arbitrary number of rows. What is the least costly way in PHP to lookup the value of Col_2 from the recordset given a value of Col_1?

Emp_ID  Col_1    Col_2
120         3       11
120         5       17
120         6        8
120         8       13
120        11       10

So for example, the pseudo-code lookup function lookup(6, $recordset) would yield 8.

Answer 1

Let's assume your recordset to array will look something like this :

Array
(
    [0] => Array
        (
            [Emp_ID] => 120
            [Col_1] => 3
            [Col_2] => 11
        )

    [1] => Array
        (
            [Emp_ID] => 120
            [Col_1] => 5
            [Col_2] => 17
        )

    [2] => Array
        (
            [Emp_ID] => 120
            [Col_1] => 6
            [Col_2] => 8
        )
    ....
)

Now create ONCE per page a search array.

$search_array =array();
foreach( $recordSet as $key=>$data ){

        $search_array[$data['Col_1']]=$data['Col_2'];   
}

Then each time you need to find the value of Col_2 from Col_1 just use :

echo $search_array[6]; // will return 8

For the other way around with the same search array use array_search()

echo  array_search("8",$search_array); // will return 6