dynamically select range of mysql columns using php - php

Question

Hello and thanks for your time!
I'm trying to pull data from a mysql table using PHP, and am fairly new to both mysql and php.
I have a table built on racing information, where the following race results are recorded:
Date, Type, WL1, L1, L2, etc up to L15
WL1 column contains a value from L1 to L15, and stands for "winning lane 1" - basically what lane the car was in that came in first place.
Columns L1 to L15 contain racers' names.
Given the above, I'm trying to display the following in a table:
Date, Type, WL1 and the value of L1 through L15 as "Winner" when the data in columns L1 through L15 match the entry in column WL1.
Example:
-----------------------------------------
Date | Type | WL1| Winner
-----------------------------------------
May 5 | Rally | 13 | John
May 7 | Stock | 2 | Stewart
May 15 | Touring | 7 | Eddy
I'm able to achieve results like this using the following code:
$sql = "SELECT * FROM races";
if($result = mysqli_query($conn, $sql)){
if(mysqli_num_rows($result) > 0){
echo "<table>";
echo "<tr>";
echo "<th>Date</th>";
echo "<th>Type</th>";
echo "<th>WL1</th>";
echo "<th>Winner</th>";
echo "</tr>";
while($row = mysqli_fetch_array($result)){
echo "<tr>";
echo "<td>" . $row['Date'] . "</td>";
echo "<td>" . $row['Type'] . "</td>";
echo "<td>" . $row['WL1'] . "</td>";
if($row['WL1'] == 'L1'){
echo "<td>" . $row['L1'] . "</td>";
}elseif($row['WL1'] == 'L2'){
echo "<td>" . $row['L2'] . "</td>";
That being said, I'm thinking there has to be an easier way than iterating through 15 values with if/elseif statements. I've tried both "while" and "for" loops with incremental values, but I only get empty results or errors, most likely due to my inexperience. I've also reproduced the above using a complex CASE statement in MySQL, but again, I'm trying to reduce lines of code.
If someone could suggest a more concise method of pulling this data, either through a MySQL statement or PHP code, I'd appreciate it. Even better if you can point to some good online examples/tutorials - the whole "teach a man to fish" thing...

Answer 1

Your data structure is what is causing your problem; you should really have a table that links racers and lanes for each race and then JOIN to that. Having said that, you can simplify your existing code by noting that the value in $row['WL1'] is the column name of the winner, so you can simply replace your if structure with:
echo "<td>" . $row[$row['WL1']] . "</td>";
I've created a sample data structure here with races, lanes and racers tables. To query from this structure you would do something like:
SELECT DATE_FORMAT(r.Date, '%b %e') AS Date, r.Type, r.Winner AS WL1, rs.Name AS Winner
FROM races r
JOIN lanes l ON l.Race = r.id AND l.Lane = r.Winner
JOIN racers rs ON rs.id = l.Racer
Which for my sample data gives:
Date Type WL1 Winner
May 5 Rally 13 John
May 7 Stock 2 Stewart
May 15 Touring 7 Eddy