Hello Roman

That's just a warning, so it's not rendering the plugin useless, but I can understand that it's annoying for you.

This is actually an improvement for the plugin, and it only occurs on tables linked to Excel, Google Sheets, XML, JSON, PHP or CSV files, or when you try to import a file that contains at least one column without a header.

It's an improvement because it's not advisable to have a column without a header - it can cause a lot of issues in the plugin, so we've added it as a warning. When the plugin creates a table from an external data source (regardless if it's linked to the data source, or imported), it's looking at the values present in the table. 

That's why we included that warning, so it tells you that the file needs to be modified, so there are no empty columns or columns without a header.

Tables linked to an existing data source are creating the structure for the table in wp_wpdatatables_columns database table, and its preferences are saved in wp_wpdatatables. The structure can't be properly configured due to these empty headers. You may be aware that SQL doesn't allow empty headers, so it's confusing (if I can use that word), what it's supposed to do with the info that doesn't exist - hence, the error.

Please go to file wp-content/plugins/wpdatatables/source/class.wdtconfigcontroller.php and on line 635 you will find this:

try {
            foreach ($dataSourceColumnsHeaders as $dataSourceColumnsHeader)
                if ($dataSourceColumnsHeader == '') throw new WDTException(__('One or more columns doesn\'t have a header. Please enter headers for all columns in order to proceed.'));
        } catch (WDTException $exception) {
            die($exception);
        }

Comment those lines, like this:

//        try {
//            foreach ($dataSourceColumnsHeaders as $dataSourceColumnsHeader)
//                if ($dataSourceColumnsHeader == '') throw new WDTException(__('One or more columns doesn\'t have a header. Please enter headers for all columns in order to proceed.'));
//        } catch (WDTException $exception) {
//            die($exception);
//        }

And it should work as it used to.

However, we will not revert this to an earlier state, so either modify the files used to generate the table so every column contains a header, or comment these lines of code each time the plugin is updated.

Hi again Roman

It's strange that you see this error on MySQL tables - they need to have origin headers by default, so you can simply remove "AS "" from the query - lose the alias, and load it with:

SELECT 
   1,
   t.spacname,
   t.industry,

...

What issues are you having with the loading speed, and is it happening on all tables, and all pages? The page load usually depends on the amount of data in the table, amount of data on the page, server performance and hosting plan.