I have three entities :


The question is how to model this in ERD? Knowing that a technician can repair multiple cars, and the same car can be repaired by one and only one technician? How should the repair entity tied to all this?

  • Would this be better asked on dba.stackexchange.com/questions ? If so, ask a moderator to migrate this question for you. – FrustratedWithFormsDesigner Nov 5 '12 at 19:21
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    What is the repair entity? so far you haven't described what it actually is, you seem to understand the relationship between technician and vehicle in both directions. – Ryathal Nov 5 '12 at 19:31

You need to specify more description of your tables and of your requirements. Anyway, here is one way to model the tables. However, in a real application there would be other things to consider. Only PKs and FKs are shown. Other columns depend on your case.

Note: In the original version of the answer, I missed the requirement that "the same car can be repaired by one and only one technician". To implement this, in the Repair_Job table, the TechID column + VIN column should be constrained to be unique.

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    Does this ensure that a vehicle is always repaired by the same technician, as asked by OP? – Manuel Lafond Mar 15 at 19:08
  • @ManuelLafond, Good point. I missed that requirement! Please check the updated solution. Thanks for pointing this out. – NoChance Mar 15 at 21:04



Note that in the ERD ( conceptual data model ) you don't specify the foreign keys, they are implicit in the relationship ( lines ).

Your data modeling tool will generate the foreing keys for you when you generate the physical data model (RDBMS dependant):



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