Here a simplified database layout

• One condo can hold multiple properties (flats, garage boxes, etc) -> 1->n relationship
• One owner can have multiple properties in the same condo and properties can have more than one owner (m->n changed to 1->n with the junction table)
• One condo can have multiple owners -> 1->n

Some additional clarification:

A owner is a member of a condo. A condo is made of properties belonging to owners BUT a owner is not linked to a property directly (there can be no relation between a property and a owner for a certain time BUT there will ALWAYS be a relation between a owner and a condo). Reason for this: the agent managing the condo will first create a list of owners and a list of properties. It is only later thet he will "link" each property to one or multiple owners (or inversely)

I'm quite new to SQL.

What SQL statements should I execute to:

• SELECT, for a specific condo (WHERE condition), the properties and their respective owners (all properties should be listed even if owners are null)
• SELECT, for a specific condo (WHERE condition), the owners along with their properties (all owners should be listed even if properties are null)
• UPDATE / DELETE existing owners (I'm uncertain about how to handle the operation for the junction tables. Should I first check if there is an entry in the junction table or not ?)
• UPDATE / DELETE existing properties (same concern)
• INSERT new owners (should I use two different SQL statements depending if the owner should be linked to a property or NOT -> IF condition ?)
• INSERT new properties (same question as above)

Could you be as clear and generic as possible so that it can be reused ? :-)