SQL files in scratches - syntax highlighting

First of all, please check that "Database Tools and SQL" plugin is enabled: https://i.imgur.com/1sI1rTq.png and correct SQL dialect is set for scratch to get proper highlighting and formatting.

Note that only basic syntax highlighting is available in scratches (https://i.imgur.com/i3UxqQK.png) as there is no information about the datasources in scratch file. That is why it is better to use database consoles for experiments: 

https://www.jetbrains.com/help/idea/working-with-database-consoles.html

Where autocomplete and syntax/errors highlighting is available