How to prevent duplicate entries in MySQL and PHP?

Please help me connecting to mysql database using php.?

• Hi guys, I have designed a very simple guestbook using a mysql database and php to link to my website but am having problems getting it going. Am fairly new to this kind of programming so I am sure its something simple ..... Basically ..... I have a mysql database called MRCADB & a table within called GUESTBOOK I have 3 php pages: GUESTBOOK.PHP ---------------------------- <table width="400" border="0" align="center" cellpadding="3" cellspacing="0"> <tr> <td><strong>Test Sign Guestbook </strong></td> </tr> </table> <table width="400" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC"> <tr> <form id="form1" name="form1" method="post" action="addguestbook.php"> <td> <table width="400" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF"> <tr> <td width="117">Name</td> <td width="14">:</td> <td width="357"><input name="name" type="text" id="name" size="40" /></td> </tr> <tr> <td>Email</td> <td>:</td> <td><input name="email" type="text" id="email" size="40" /></td> </tr> <tr> <td valign="top">Comment</td> <td valign="top">:</td> <td><textarea name="comment" cols="40" rows="3" id="comment"></textarea></td> </tr> <tr> <td> </td> <td> </td> <td><input type="submit" name="Submit" value="Submit" /> <input type="reset" name="Submit2" value="Reset" /></td> </tr> </table> </td> </form> </tr> </table> <table width="400" border="0" align="center" cellpadding="3" cellspacing="0"> <tr> <td><strong><a href="viewguestbook.php">View Guestbook</a> </strong></td> </tr> </table> [THAT SEEMS TO WORK FINE & OFFER A PAGE TO ENTER THE MESSAGE ETC] ADD GUESTBOOK.PHP ------------------------------------ <?php $host="localhost"; // Host name $username="myusername"; // Mysql username $password="mypassword"; // Mysql password $db_name="mrcadb"; // Database name $tbl_name="guestbook"; // Table name // Connect to server and select database. mysql_connect("$host", "$username", "$password")or die("cannot connect server "); mysql_select_db("$db_name")or die("cannot select DB"); $datetime=date("y-m-d h:i:s"); //date time $sql="INSERT INTO $tbl_name(name, email, comment, datetime)VALUES('$name', '$email', '$comment', '$datetime')"; $result=mysql_query($sql); //check if query successful if($result){ echo "Successful"; echo "<BR>"; echo "<a href='viewguestbook.php'>View guestbook</a>"; // link to view guestbook page } else { echo "ERROR"; } mysql_close(); ?> and then finally: VIEWGUESTBOOK.PHP ------------------------------------- <table width="400" border="0" align="center" cellpadding="3" cellspacing="0"> <tr> <td><strong>View Guestbook | <a href="guestbook.php">Sign Guestbook</a> </strong></td> </tr> </table> <br> <?php $host="localhost"; // Host name $username="myusername"; // Mysql username $password="mypassword"; // Mysql password $db_name="mrcadb"; // Database name $tbl_name="guestbook"; // Table name // Connect to server and select database. mysql_connect("$host", "$username", "$password")or die("cannot connect server "); mysql_select_db("$db_name")or die("cannot select DB"); $sql="SELECT * FROM $tbl_name"; $result=mysql_query($sql); while($rows=mysql_fetch_array($result)… ?> <table width="400" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC"> <tr> <td><table width="400" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF"> <tr> <td>ID</td> <td>:</td> <td><? echo $rows['id']; ?></td> </tr> <tr> <td width="117">Name</td> <td width="14">:</td> <td width="357"><? echo $rows['name']; ?></td> </tr> <tr> <td>Email</td> <td>:</td> <td><? echo $rows['email']; ?></td> </tr> <tr> <td valign="top">Comment</td> <td valign="top">:</td> <td><? echo $rows['comment']; ?></td> </tr> <tr> <td valign="top">Date/Time </td> <td valign="top">:</td> <td><? echo $rows['datetime']; ?></td> </tr> </table></td> </tr> </table> <BR> <? } mysql_close(); //close database ?> --------------------------------------… Im sure that seems fairly straight forward to you php geniuses! I have linked the GUESTBOOK.PHP page to my index and when you click onto the link it comes up with the form to add to the guestbook - as I expected. When I try adding to the guestbook I get an error message that reads "CANNOT SELECT DB" Further - if I try to view ADDGUESTBOOK.PHP or VIEWGUESTBOOK.PHP I get the same message. It is obvious that it cannot select the database .... i'm just not sure why! Am I right in thinking that it is connecting to mysql but not finding the database within? I have set up the mysql on my web server etc - it must just be something small! Aggggghhhhhhhh! Any idea's?! Ta in advance! :S PS ... I know that I have used some capitals etc in this message. In my script everything is lowercase so please dont offer that as an answer! :)

• Answer:

  The code should work (I believe) so perhaps you have the wrong name of the database? I would suggest modifying your code as follows to find out the real problem: FROM: mysql_select_db("$db_name")or die("cannot select DB"); TO mysql_select_db("$db_name")or die("cannot select DB ". mysql_error());