Intermittent "No Database Selected" in PHP/MySQL?

Question

Have a PHP/MySQL form with a dropdown box containing a list of 350 names. When any random name is selected, sometimes it works & displays info about that name from the database, and sometimes the form gives the error "No Database Selected".

Here's what I've tried, pretty much grasping at straws as I'm not a programmer:

Increasing max_connections in /etc/my.cnf from 200 to 2000 (even though only 4-5 connections are made and it's a lightly used server)
Changing mysql_pconnect to mysql_connect
Adding the word true to this connection string:

$mysql = mysql_pconnect($hostname_mysql, $username_mysql, $password_mysql, true) or trigger_error(mysql_error(),E_USER_ERROR);
Changing the word require_once to require on this line:

[?php require('/home/user/Connections/mysql.php'); ?]
Enabling MySQL & PHP query & error logging. (no errors logged)

~~Here is the code: [removed old bad code]~~

Update: Working answer from Rob Apodaca below.

Are you sure that your mysql_select_db call actually always contains a database to select? Make a test output of $mysql to see whether there are instances when it is empty. — Pekka
– Pekka, Commented May 6, 2010 at 15:52
I added echo $mysql; and it gives me "Resource Id #3". I added some additional error handling and it gives me: SQL Error [256] (1046) No database selected Query : SELECT * FROM tbl LIMIT 1 On line 65, PHP 5.1.6 (Linux) — ANE
– ANE, Commented May 6, 2010 at 16:11

Rob Apodaca · Accepted Answer · 2012-09-19 08:10:02Z

3

This line: mysql_select_db($database_mysql, $mysql); appears more than once in your provided script. Since the value of $database_mysql does not appear to change, I would remove all of the instances of that line and place it just after the mysql_pconnect/mysql_connect line.

edited Sep 19, 2012 at 8:10

user647772

answered May 6, 2010 at 16:33

Rob Apodaca

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1 Comment

ANE Over a year ago

This appears to have worked. After editing both files exactly as you suggested, I tested selecting random names in the dropdown box over and over and every time, it's working with no errors. Am getting a couple other people to test and to make absolutely sure, but so far I'm confident in your fix. Thanks so much Rob! (BTW, cool last name too.)

khr055 · Accepted Answer · 2012-12-03 16:49:42Z

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My issue was with a database connection object (B) that was serialized within another serialized object (A). Sometimes, depending on what had happened prior to object A being unserialized, object B would perform a mysql_select_db() call with a null database name as it had been lost.

We littered our code with some echo's of the result of a MySQL query "SELECT DATABASE()" until we found where the intermittent loss of the default database was occurring. Hope this helps!

edited Dec 3, 2012 at 16:49

khr055

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answered Dec 28, 2010 at 15:20

John

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