Lets say, I have at the moment, the following tables:

categories

• id
• name (for example "museum", "tower" or "theater")
• some other fields...

countries

• id
• name
• some other fields...

cities

• id
• name
• country_id
• some other fields...

sights

• id
• name
• city_id
• category_id
• some other fields...

My question / problem

Now I want to combine all these table into a single table which I call "objects". Since the different tables avove haven't the same "some other fields.."-Fields, I need a flexible way of storing this data. There are 2 options:

• Storing it as a json-string in a field called "data" in the object-table
• Or storing it in a separete table "properties" (object_id, field_name, field_value)

My Questions:

• But which version would be better/has a better performace? "Json to Object conversion in PHP and string-search" vs "multiple joins"?
• For the second version: Which datatype should the field "field_value" have? This value can be filled with anything. From a boolean value to strings.