how to find first column name with null value in specific row

Question

The query below works fine for returning the column names that are null, what I am trying to accomplish is have it return to the first column name with a null value. I also have another column named email that has a unique email address for each row. My problem is I cannot figure out the appropriate syntax for doing this. any help is appreciated!

I am also using php5.2 for this.

 SELECT col FROM (SELECT 'GAME0' AS col, GAME0 AS value FROM USERNAME
       UNION ALL SELECT 'GAME1', GAME1 FROM USERNAME
       UNION ALL SELECT 'GAME2', GAME2 FROM USERNAME
       UNION ALL SELECT 'GAME3', GAME3 FROM USERNAME
       UNION ALL SELECT 'GAME4', GAME4 FROM USERNAME
       UNION ALL SELECT 'GAME5', GAME5 FROM USERNAME
       UNION ALL SELECT 'GAME6', GAME6 FROM USERNAME
       UNION ALL SELECT 'GAME7', GAME7 FROM USERNAME
       UNION ALL SELECT 'GAME8', GAME8 FROM USERNAME
       UNION ALL SELECT 'GAME9', GAME9 FROM USERNAME
       UNION ALL SELECT 'GAME10', GAME10 FROM USERNAME
       UNION ALL SELECT 'GAME11', GAME11 FROM USERNAME
       UNION ALL SELECT 'GAME12', GAME12 FROM USERNAME
       UNION ALL SELECT 'GAME13', GAME13 FROM USERNAME
       UNION ALL SELECT 'GAME14', GAME14 FROM USERNAME
       UNION ALL SELECT 'GAME15', GAME15 FROM USERNAME
       UNION ALL SELECT 'GAME16', GAME16 FROM USERNAME
       UNION ALL SELECT 'GAME17', GAME17 FROM USERNAME
       UNION ALL SELECT 'GAME18', GAME18 FROM USERNAME
       UNION ALL SELECT 'GAME19', GAME19 FROM USERNAME
    ) allValues 
    WHERE value is null and email='emailaddress'

EDIT: if the query above is unneeded, I need something like below, where I can change the value of the first null value. Again syntax is my biggest problem.

update username
SET CASE GAME0
    WHEN GAME0 IS NOT NULL THEN GAME1
    WHEN GAME1 IS NOT NULL THEN GAME2
    WHEN GAME2 IS NOT NULL THEN GAME3
    WHEN GAME3 IS NOT NULL THEN GAME4
    WHEN GAME4 IS NOT NULL THEN GAME5
    WHEN GAME5 IS NOT NULL THEN GAME6
    WHEN GAME7 IS NOT NULL THEN GAME8
    WHEN GAME8 IS NOT NULL THEN GAME9
    WHEN GAME9 IS NOT NULL THEN GAME10
    WHEN GAME10 IS NOT NULL THEN GAME11
    WHEN GAME11 IS NOT NULL THEN GAME12
    WHEN GAME12 IS NOT NULL THEN GAME13
    WHEN GAME13 IS NOT NULL THEN GAME14
    WHEN GAME14 IS NOT NULL THEN GAME15
    WHEN GAME15 IS NOT NULL THEN GAME16
    WHEN GAME16 IS NOT NULL THEN GAME17
    WHEN GAME17 IS NOT NULL THEN GAME18
    WHEN GAME18 IS NOT NULL THEN GAME19
  END where EMAIL='emailaddress'

Answer 1

You can make this query much simplier and do some of the calculations through php:

$arr_field = array();
foreach(range(0, 19) as $i)
    $arr_field[] = "GAME{$i}";

$str_add = implode(' + ', $arr_field);
$str_select = implode(', ', $arr_field);

$query = 
mysql_query("
    SELECT {$str_select}
    FROM USERNAME
    WHERE ({$str_add}) IS NULL AND email = 'emailaddress'
");

// Then get the NULL column through a loop

while($row = mysql_fetch_assoc($query))
    foreach($arr_field as $h)
        if ( ! isset($row[$h])) {

            echo "Found column! {$h}<br />";
            break;

        }

Baiscly I add all the 20 fields together, and if any of these 20 values are NULL, the result becomes NULL. I fetch all 20 values, then loop through php to find NULL fields.

To be honest though, I would have made another stucture having a second table handling these GAME0 - GAME19 fields instead.

Answer 2

I don't really understand your table structure, but here is an easy way: just add order by col limit 1 to your query.

Edit: for this to work, you will have to use "GAME00", "GAME01" etc. (You don't have to change the column names, just the name you place in the string)

Edit 2: To include the email address it has to exist in your subquery, like this:

SELECT col FROM (SELECT 'GAME00' AS col, GAME0 AS value, email FROM USERNAME
   UNION ALL SELECT 'GAME01', GAME1, email FROM USERNAME

(etc)