Postgis - merge feature classes and check overlaps and holes

Job ID: 34558674

Budget: $10 – $20 USD

Dear POSTGIS expert. I need query (SQL) to generate table or view (preferred) with overlapping features or holes.
I've 12 feature classes (12 postgres tables) with polygon data. I need to check if they cover all dataset range.
I need to detect overlapping features and places without any feature. It is possible, to should be database view. If we agree I'll pay exactly amount we agree. I'll pay only if script will work.