MySQL query problem

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Warning: mysql_fetch_* expects parameter 1 to be resource, boolean given error

 $result3=mysql_query("select * from $mail ORDER BY `data_id` DESC"); 

in this case if data_id is NULL query is showing Warning - Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in F:xampphtdocs...

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If mysql_query fails, it returns false . You need to check that before you pass $result3 to any other mysql function. (Also print or log the error in that case so you can debug it.)

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As it describes in the official document,

For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.

So the parameter 1 is false

See: http://php.net/manual/en/function.mysql-query.php

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