[RESOLVED] No index defined

Wales

I'm starting to learn php and mysql. I edited the code below I copied from a website and had a few questions.

When I look at myphpadmin it says no index defined. What does that mean? How do I add an index to the following script when I add tables to the database?

Why do I need a ! in front of $con in the if statement?

<?php
$con = mysql_connect("localhost","root","password");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }// Create database
if (mysql_query("CREATE DATABASE main",$con))
  {
  echo "Database created";
  }
else
  {
  echo "Error creating database: " . mysql_error();
  }// Create table in my_db database
mysql_select_db("main", $con);
$sql = "CREATE TABLE categories
(
solid varchar(15),
electronics varchar(15),
apparel varchar(15)
)";
if ($sql)
	{
	echo "<br />Table and categories created";
	}
mysql_query($sql,$con);mysql_close($con);
?>

laserlight

When I look at myphpadmin it says no index defined. What does that mean? How do I add an index to the following script when I add tables to the database?

An index is like a book index: it allows for fast searching based on the key provided. Your table should have a primary key (which is automatically an index). This could be a column or a group of columns.

However, it looks like you are very mistaken in your understanding of relational databases. Let's take a look at your CREATE TABLE statement:

CREATE TABLE categories
(
solid varchar(15),
electronics varchar(15),
apparel varchar(15)
)

So, each category has a "solid", an "electronics" and an "apparel". This does not make sense. I am not sure what is "solid" in this context, but "electronics" and "apparel" sound like categories to me, not attributes of a category.

Why do I need a ! in front of $con in the if statement?

If you read the PHP manual concerning [man]mysql_connect/man, you will find that it returns false if the attempt to connect failed. As such, $con would be false, thus !$con would be true, hence it is logical to display a message informing the user of the problem.

If you have no idea what ! means, read the PHP manual on Logical Operators.

Wales

Wow your awesome! thanks.

monkeyt

I had -- no index defined -- I clicked on go and saved the siteurl as a primary index -- is it safe to do this? If not do I just choose a random primary our index?

I did this for my 3 sites as are all on the same server and differ only by .com, .co, .info and database name,password etc (prefix being the same in config.php) - will this cure the problem of the categories in the .com site coming up in the .co and .info site - as I am getting fed up with rewriting the categories after I re-open the sites - the .com original cats keep showing in the others.

Thanks

thanks in advance for your help