Loop in column name MYSQL - mysql

Question

I am using MYSQL.My table contains column name as Revenue2000,Revenue2001,Revenue2002,....,Revenue 2016,Revenue 2017
Traditional way(to select all column manually):
select Revenue2005,
Revenue2006,
Revenue2007,
Revenue2008,
Revenue2009,
Revenue2010
from table_name
Desired Way:
I want to write a Dynamic select statement .There should 2 variables "start" and "end" so that i can make it dynamic.User has the option to specify the starting year and ending year and can view the desired result.
In above case, Start year =2005
End Year=2010

Answer 1

Yes, it's bad database design, and the best answer would be "don't do this at all, just fix your table." Unfortunately, sometimes you're stuck with something someone else made, and can't change it for whatever reason, but you still need to accomplish something (welcome to my life). I would do it like this:
Get the years from user input and convert them to integers in case someone enters something silly/naughty. Don't depend on client-side validation. Prepared statements won't help you here because these will be used as parts of column names.
$start = (int) $_POST['start'];
$end = (int) $_POST['end'];
Do a quick sanity check to make sure that the range makes sense and should work with what's in your database.
if ($start > $end
|| $start < $lowest_year_in_your_db
|| $end > $highest_year_in_your_db) {
// quit with error
}
Then you can generate a list of columns to use in your query. Here's one way with range and array_map, but you could also just build a string with a for loop.
$columns = implode(', ', array_map(function($year) {
return "Revenue$year";
}, range($start, $end)));
$sql = "SELECT $columns FROM table_name";
Theoretically, the worst thing that should be able to happen with this is that you'd get a column that didn't exist, and your query would fail.
But really, if you have any choice about it, don't do this. Normalize your database as people have stated in the comments, or find whoever keeps adding more year columns to the database and make them do it.

Answer 2

As already pointed out the database design is horrible. You should really normalize it, it's worth the effort.
However if that is not possible at the moment the follow code should do exactly what you need:
// Connect to DB
$mysqli = new mysqli("localhost", "USERNAME", "PASSWORD", "DATABASE");
// Get column names
$columns = $mysqli->query('SHOW COLUMNS FROM revenue')->fetch_all();
$columnNames = array_column($columns, 0);
// Extract years from column names
$years = array_map(function($columnName) {
return (int) substr($columnName, -4);
}, $columnNames);
// Get max and min year
$maxYear = max($years);
$minYear = min($years);
// Input year start and end
$start = (int) $_POST['start']; // User-input
$end = (int) $_POST['end']; // User-input
// Avoid wrong inputs
if($start > $end || $start < $minYear || $end > $maxYear) {
die('Error');
}
// Create the SQL-query
$selectColumns = [];
for ($i = $start; $i <= $end; $i++) {
$selectColumns[] = "revenue" . $i;
}
$queryString = "SELECT " . implode(", ", $selectColumns) . " FROM TABLE";
// Run the query
// ...