Hi, Chris 

Firstly, I would like to sincerely apologize for the delayed response as we have been experiencing an unusually high number of tickets. I am sorry that it has taken longer than usual to respond to your concern and your patience is highly appreciated.

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As the custom posts/fields, are a part of the WordPress database;

pulling this data can only be done through MySQL query-based tables.

Please note: Using this plugin feature requires at least a basic knowledge of SQL. It is assumed that you can create the table in some MySQL data manager (e.g., PHPMyAdmin, MySQL Workbench), and prepare a SQL query that will return the data you need. 

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A good way to achieve this can be experimenting using our WPDB SQL Query Constructor tool.

- Please note: this tool is not an ultimate query generator. 

It simply constructs a suggestion of a query. We are constantly working to improve it, but SQL is such a complicated and flexible language that full automation for constructing queries is next to impossible. 

Consequently, the more complicated the query, the higher is the probability that it will not return exactly what you need. So, you will often need to play around with the resulting query.

Please be advised that writing custom SQL Queries or debugging Queries does not fall under what our support covers.

You can check out this official page of WP codex,  for help with writing custom Queries.

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I am not able to reproduce the issue as you described it.

If i try to simply select a few columns from the "posts" database table, it correctly loads a preview in the Constructor, and i can see it without any errors.

Here are the screenshots of the columns i selected :

But when i compare that with your screenshots, there is an INNER JOIN, and also there is a column from "wp_users" table, so i am not sure exactly which tables , columns you chosen, and if you added some relation between tables,  or conditions, in the Constructor.

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Here is my Video recording, how it looks from our end when we just make a simple Query from Posts.

https://watch.screencastify.com/v/4gSaToilS5YRONXdIpdT

Could you please record your screen or show me some screenshots of which tables and columns ( any conditions added)  you have selected in the Constructor?

Thank you