使用for循环从MySQL查询中逐步选择值

Question

I am trying to use a for loop to select an incremental value with a MySQL query. I have included sample code below:

<?php

$day_1="sep_28";
$day_2="sep_29";
$day_3="sep_30";

$query = mysql_query("SELECT * FROM table WHERE id = '$id'");

while ($row = mysql_fetch_assoc($query))
{
for ($i = 1; $i <= 3; $i++) 
    {
        $dayVar = "day_".$i;
        //$dayVarCount = $dayVar."_count"; // Don't really need this anymore, so removed.
        $dayVarCount = $row[$$dayVar];
        echo "$$dayVar.': '.$dayVarCount<p>"; // Edited.
    }      
}
?>

I think I am getting close, but when I run the code my page is showing this:

$day_1.': '.0

$day_2.': '.2

$day_3.': '.5

Any additional recommendations? Thanks for the great help!

Answer 1

Try a variable variable:

for ($i = 1; $i <= 3; $i++) 
{
    $dayVar = "day_".$i;
    $dayVarCount = $dayVar."_count";
    $$dayVarCount = $row[$$dayVar];
    echo $$dayVar.': '.$$dayVarCount.'<p>'; // Edited.
}

This basically uses a string to reference a variable by its name.

Just think of it this way:

$variable = 'hello';

$string = 'variable';

echo $$string;
// Is the same thing as:
echo $variable;

// Because you can thing of $$string as ${$string} ---> $variable when {$string} is interpreted into 'variable'

http://php.net/manual/en/language.variables.variable.php