Is there Such Thing As The Opposite of Unique Constraint
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
asked 39 secs ago
JDGale8JDGale8
1
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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
asked 39 secs 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.
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
asked 39 secs 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.
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
postgresql constraint
asked 39 secs 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 39 secs 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 39 secs 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 39 secs ago
JDGale8JDGale8
1
asked 39 secs ago
JDGale8JDGale8
1
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.
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.
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