philipxy questions

philipxy answers

• Can I use the same foreign key constraint in two different tables?
• How to add reference to a non primary key column of a table in rails5
• PostgreSQL using constants in foreign key
• Is there a well-defined difference between "normalizing" and "canonicalizing" data?
• Find date range overlaps within the same table, for specific user MySQL
• Relational algebra to count rows
• How to represent GROUP BY with HAVING COUNT(*)>1 in relational algebra?
• relationships between 3 entities in ER diagram--is a ternary enough or are 2 binaries also needed?
• When should I use a composite primary key?
• SQL plan compilation and truth tables