Question

I have some tables that benefit from many-to-many tables. For example the team table.

Team member can hold more than one ‘position’ in the team, all the positions are listed in the position db table. The previous positions held are also stored for this I have a separate table, so I have

• member table (containing team details)
• positions table (containing positions)
• member_to_positions table (id of member and id of position)
• member_to_previous_positions (id of member and id of position)

Simple, however the crux comes now that a team member can belong to many teams aghhh.
I already have a team_to_member look-up table.
Now the problem comes how do I tie a position to a team? A member may have been team leader on one team, and is currently team radio man and press officer on a different team. How do I just pull the info per member to show his current position, but also his past history including past teams.
Do I need to add a position_to team table and somehow cross reference that, or can I add the team to the member to positions table?

It’s all very confusing, this normalization.

Answer 1

It’s perfectly legitimate to have a TeamPositionMember table, with the columns

Team_Id
Position_Code
Member_Id
Start_Date
End_Date NULLABLE

And and a surrogate ID column for Primary Key if you want; otherwise it’s a 3-field composite Primary Key. (You’ll want a uniqueness constraint on this anyway.)

With this arrangement, you can have a team with any set of positions. A team can have zero or more persons per position. A person can fill zero or more positions for zero or more teams.

EDIT:

If you want dates, just revise as shown above, and add Start_Date to the PK to allow the same person to hold the same position at different times.