How do I skip an item in while loop if variable empty?

You can use continue control structure for skip an iteration. Please read the docs

Example:

if(!$row['tweet']) {  continue;}

php mysql sql

You could also not return rows without information in tweet1, this would make the php check for data in tweet1 unnecessary.

$query = mysql_query("SELECT * FROM $DBtable WHERE tweet1 IS NOT NULL ORDER BY time");

php mysql sql

if (empty($row['tweet'])) {    continue;}

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