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0

I want to be constrain my database with what is essentially the opposite of a UNIQUE constraint. I want to only be able to add a new row if some combination of fields has been added before.

Note: I am working within postgres.

Take the following datasets for example. I want a "NON UNIQUE" constraint on the following:

1, a, 1



1, a, 1



1, b, 1

I should not have been able to add the row (1, b, 1) since it has not appeared before. There are also other fields I don't want to constrain so it's not like all the entries are identical.

This may be a separate question, but I would also like to add the constraint that all rows with the same value in one column (i.e. a in the above example) have the same value in another.

So I want this to be impossible

1, a, 1



1, a, 1



0, a, 1

But this is ok

1, a, 1



1, a, 1



0, b, 1

I have looked around pretty heavily and the opposite of this is possible
with unique constraints, but I can't find anything that works for this.
Check constraints will only look at the row in question, and won't take into account the entire table's entries like a unique constraint would.

Is this even possible? Or is this now out of the realms of Postgres functionality, and must be done in-application.

postgresql constraint

share

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is one valid and the other is not?
  
  – Michael Kutz
  2 mins ago
  

  
  
  
  

add a comment | 

0

I want to be constrain my database with what is essentially the opposite of a UNIQUE constraint. I want to only be able to add a new row if some combination of fields has been added before.

Note: I am working within postgres.

Take the following datasets for example. I want a "NON UNIQUE" constraint on the following:

1, a, 1



1, a, 1



1, b, 1

I should not have been able to add the row (1, b, 1) since it has not appeared before. There are also other fields I don't want to constrain so it's not like all the entries are identical.

This may be a separate question, but I would also like to add the constraint that all rows with the same value in one column (i.e. a in the above example) have the same value in another.

So I want this to be impossible

1, a, 1



1, a, 1



0, a, 1

But this is ok

1, a, 1



1, a, 1



0, b, 1

I have looked around pretty heavily and the opposite of this is possible
with unique constraints, but I can't find anything that works for this.
Check constraints will only look at the row in question, and won't take into account the entire table's entries like a unique constraint would.

Is this even possible? Or is this now out of the realms of Postgres functionality, and must be done in-application.

postgresql constraint

share

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is one valid and the other is not?
  
  – Michael Kutz
  2 mins ago
  

  
  
  
  

add a comment | 

I want to be constrain my database with what is essentially the opposite of a UNIQUE constraint. I want to only be able to add a new row if some combination of fields has been added before.

Note: I am working within postgres.

Take the following datasets for example. I want a "NON UNIQUE" constraint on the following:

1, a, 1



1, a, 1



1, b, 1

I should not have been able to add the row (1, b, 1) since it has not appeared before. There are also other fields I don't want to constrain so it's not like all the entries are identical.

This may be a separate question, but I would also like to add the constraint that all rows with the same value in one column (i.e. a in the above example) have the same value in another.

So I want this to be impossible

1, a, 1



1, a, 1



0, a, 1

But this is ok

1, a, 1



1, a, 1



0, b, 1

I have looked around pretty heavily and the opposite of this is possible
with unique constraints, but I can't find anything that works for this.
Check constraints will only look at the row in question, and won't take into account the entire table's entries like a unique constraint would.

Is this even possible? Or is this now out of the realms of Postgres functionality, and must be done in-application.

postgresql constraint

share

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

1, a, 1



1, a, 1



1, b, 1

1, a, 1



1, a, 1



0, a, 1

1, a, 1



1, a, 1



0, b, 1

share

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 mins ago

JDGale8JDGale8

1

New contributor

JDGale8 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 mins ago

JDGale8JDGale8

1