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Editorial Team
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Asked: 2026-05-16T05:10:30+00:00

I have to work with a database to do reporting The DB is quite

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I have to work with a database to do reporting
The DB is quite big : 416 055 104 rows
Each row is very light though, just booleans and int ids.

Each row is identify by 3 columns, but at my surprise, there is no Primary Key on it.
Only a Clustered Index with a unique constraint.

So Knowing that, I have 2 question.

  1. Could there be ANY good reason for that?
  2. Is there any way I can turn this into a primary key.

Regarding question 2

Creating a new primary key also creates a non-clustered index to associate with (there is already an existing clustered one).
This is not what I am looking for. I want to keep that same index, but also make it a primary key.

  • Is it possible?
  • Would that be faster that creating the whole index again? (I hope so)
  • What could be the consequences? (locks? crash? corrupted data?)
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1 Answer

  1. Editorial Team

    There is little or no difference between a PRIMARY KEY and a UNIQUE constraint on non-nullable columns. So if the columns in question are non-nullable then I suggest you do nothing. The main reason to make a candidate key into a primary key is if you have some software (such as a data modelling tool or other development tool) that expects the key to be identified with a PRIMARY KEY constraint.

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