Debugging MySQL

There are two very easy ways to debug your MySQL queries. If you are trying to do a MySQL query and it isn't working, you will want to try these:

1) If you are trying to create queries dynamically by inserting PHP variables into your MySQL queries, such as

$myQuery = "select * from blogcomments where blogpost_id={$blogPostId} order by created asc";
$result = mysql_query($myQuery);

where $blogPostId is a PHP variable you are trying to insert into your MySQL statement, make sure that the variable has the value you think it does. You can easily check this by printing out that whole statement to the browser.

$myQuery = "select * from blogcomments where blogpost_id={$blogPostId} order by created asc";
echo $mQuery; //print what this query really looks like after the variable is inserted
$result = mysql_query($myQuery);

If the query shows up as "select * from blogcomments where blogpost_id= order by created asc", you now know that the $blogPostId variable is empty.

2) use PHP's mysql_error() function to display any errors thrown by MySQL after you run the query:

$myQuery = "select * from blogcomments where blogpost_id={$blogPostId} order by created asc";
$result = mysql_query($myQuery);
echo mysql_error(); //print out any errors thrown by MySQL