php variable is treated like string - php

Question

I have this issue.
I need to receive, from comments column in mysql database, a string like this:
WHERE IDTable=$number
When i get this comment i have to put it like a Where clause in my query.
But if i write this code
$where=getComment($table,$field); //I get the string i wrote above
$number=5; //I initialize $number in my code
$sql="SELECT * FROM table $where";
print "SQL: $sql";
i get this:
SELECT * FROM table WHERE IDTable=$number
obviously i'd like to have in response:
SELECT * FROM table WHERE IDTable=5
How can I do that?
Thanks

Answer 1

I strongly suspect that the code you have a problem with is not the same code as above, as the above would not produce the result you stated. At the very least you are missing the definition of the function you're calling, to create said output.
However, what would produce such a result is by using single quotes around a string. Which prevents variable expansion, and treats them as regular strings instead.
Not only that, but your code is out of order as well. You cannot use a variable before you have declared it, as it simply does not exist yet.

Answer 2

The string returned by getComment() will not be parsed, so any PHP variables in it ($number) will be returned as the literal string.
I can think of two options -
1
Allow an extra parameter for getComment() so you can pass it $number
$number=5;
$where = getComment($table,$field,$number); // returns "WHERE IDTable=5"
$sql="SELECT * FROM table $where";
2
Do not return $number from getComment(), then you can add it when you build the query.
$where=getComment($table,$field); // returns "WHERE IDTable="
$number=5;
$sql="SELECT * FROM table $where $number";

Answer 3

Perhaps the String Value you got from MySQL: WHERE IDTable=$number may have been enclosed within Single Quotes. Consider the Example Below.
$number = 22;
$str = 'WHERE IDTable=$number';
var_dump($str); //<== YIELDS:: 'WHERE IDTable=$number' B'COS IT'S IN SINGLE QUOTES
$parts = explode("=", $str);
list($where, $var) = $parts;
$var = ltrim(trim($var), "\$");
$newStr = trim($where . "=" . $$var);
var_dump($$var); //<== YIELDS:: int 22
var_dump($newStr); //<== YIELDS:: 'WHERE IDTable=22' (length=16)
Assuming this is the case with your String; to get around that, You may simply want to extract the Variable from the String and then rebuild the String as the Snippet above demonstrates. Otherwise; if you have a possibility of enclosing the String in Double Quotes, this convoluted work-around would be utterly irrelevant.