Loop Not Working. Please Help

[SP8600]

Could some one have a look at this loop and tell me what is wrong with it please.

$replace_sqlquery = "SELECT oldtxt,newtxt FROM changetxt";
$replace_result = mysql_query($replace_sqlquery);
$replace_number = mysql_num_rows($replace_result);
$replace_row = mysql_fetch_assoc($replace_result);
$content_replace = $page_row['main_content']; 

while ($x = mysql_fetch_array($replace_result)) { 
$content_replace = str_replace ("$x[oldtxt]","$x[newtxt]","$content_replace"); 
$replace_row = mysql_fetch_assoc($replace_result);
}

[RedDragon]

your loop fails seen from logical aspects,

you are fetching the rows from your query 3 times? why

also content_replace does not seem to be set

try with this code:

// define $page_row['main_content']

$content_replace = $page_row['main_content'];

$replace_sqlquery = "SELECT oldtxt,newtxt FROM changetxt";
$replace_result = mysql_query($replace_sqlquery);

while ($x = mysql_fetch_array($replace_result)) { 
$content_replace = str_replace ("$x[oldtxt]","$x[newtxt]",$content_replace); 
}

echo $content_replace;