How to implement content from external database into WordPress text page? [closed]

You should write a plugin, or compact the code needed for this in a child theme functions.php.
About pulling data from external databases: the simplest way is to use php built-in functions.
I would proceed this way:

1. Register a shortcode to place your table wherever you want in WordPress, you probably want to pass some values, to select the specific data you want to pull from the database or the look the table should have
2. Hook the shortcode to a function, that connects to the external db and queries it, according to your needs, builds a table using the data and outputs it.

Resources:
WordPress Shortcodes,
Html table output via php