How to sum values ​​with the same array value in PHP

Question

I merged two arrays (both taken from different mysql tables) and now I want to sum all elements in the arrays with the same value.

$merged_arr = array_merge($reg, $rel);

Array
(
    [0] => Array
        (
            [DEPARTMENT] => LEAFSPRINGDIRECT
            [BASIC INCOME] => 3035.37
            [OT PAY] => 0
        )

    [1] => Array
        (
            [DEPARTMENT] => MUFFLERDIRECT
            [BASIC INCOME] => 24962.09
            [OT PAY] => 5358.76
        )

    [2] => Array
        (
            [DEPARTMENT] => MUFFLERDIRECT 
            [BASIC INCOME] => 14082.080000000002
            [OT PAY] => 3248.4
        )
)

This is what I tried, but I had to use if-else statements over and over again.

foreach($merged_arr as $key => $val) 
    {
        // echo $val['BASIC INCOME']."<br>";

        // echo array_keys(array_values($new_arr)[$key])[$count]."-".array_values(array_values($new_arr)[$key])[$count]."<br>";
        if(array_values(array_values($new_arr)[$key])[$count] == "RADIATORDIRECT") {
            $new_arr['BASIC INCOME'] += '...';
        }

        $count++;
    }

The array I want should be like this:

Array
(
    [0] => Array
        (
            [DEPARTMENT] => LEAFSPRINGDIRECT
            [BASIC INCOME] => 3035.37
            [OT PAY] => 0
        )

    [1] => Array
        (
            [DEPARTMENT] => MUFFLERDIRECT
            [BASIC INCOME] => 39044.17‬
            [OT PAY] => 8607.16‬
        )
)

Is there any easier way? Thank you in advance.

Answer 1

I would do this on the SQL side:

SELECT DEPARTMENT, SUM(`BASIC INCOME`) AS `BASIC INCOME`,  SUM(`OT PAY`) AS `OT PAY`
FROM
(
    SELECT DEPARTMENT, `BASIC INCOME`, `OT PAY`
    FROM `table_a`
    -- WHERE ...

    UNION ALL

    SELECT DEPARTMENT, `BASIC INCOME`, `OT PAY`
    FROM `table_b`
    -- WHERE ...
    
) UNIONS

GROUP BY DEPARTMENT