We have faced strange issue with MySql old version (version 4).
Our php file will pass a querystring variable "id". It can have a value or it can be empty in some situation.
Initially, we used below code,
$sql="select school_name from school_table where id=$id";
It was working fine if the $id is assinged with a value.
It showed syntax error if $id is not having any value.
Below workaround resolved the issue.
Added below code above the query.