PHP number: decimal point visible only if needed

As Emil says yours are good. But if you want to remove 0 from e.g. 7.50 too, I've got a suggestion, rtrim():

<?php
    // if $sql_result["col_number"] == 1,455.50
    rtrim(rtrim(number_format($sql_result["col_number"], 2, ".", ""), '0'), '.');
    // will return 1455.5
?>

floatval or simply casting to float

php > echo floatval(7.00);
7
php > echo floatval(2.30);
2.3
php > echo floatval(1.25);
1.25
php > echo floatval(1.125);
1.125

php > echo (float) 7.00;
7
php > echo (float) 2.30;
2.3
php > echo (float) 1.25;
1.25
php > echo (float) 1.125;
1.125

I actually think that your workaround is as good as any. It's simple and clear, and there's really no point talking about performance here, so just go for it.