Question

I have a table with contacts and another one with message. In the message table I have a cell where I keep a serialized string of IDs of those members that the message was sent to.

Now, I am going to append a unique identifier token and when a member responds I’ll be able to track which member it is. Shall I store this info in a separate table, or add another cell to message tables, which can also hold a string of responded members?

Logic tells me that a separate table would be easier, but at the same time it can grow pretty fast as there could be multiple groups of recipients of messages, and each can have multiple messages, which will translate into multiple rows, as opposed to a single cell with a serialized string.

Answer 1

I think the conventional approach would be to have join tables. So if you have a Contacts table and a Messages table, you could create a ContactMessagesSent table, which has the primary keys of both Contacts and Messages as columns, to keep track of which messages were sent to which contacts. You could create another join table ContactMessagesReceived to track responses.

So

ContactMessagesSent
--------
contact_id ; // primary key of Contacts
message_id ; // primary key of Messages
...

If you use proper indexing, it will perform well even if there are lots of rows in the table.