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Thread: add constraints to views

add constraints to views

From
Andreas Fromm
Date:
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Please consider the following situation.

CREATE TABLE test_table (
~    id SERIAL PRIMARY_KEY,
~    tag BOOLEAN,
~    field1 INTEGER
);

CREATE VIEW test_view (
~    SELECT * FROM test_table WHERE tag
);

Now I want ad a NOT NULL constraint to the view on field1. I tryed the
following, but neither works.

ALTER TABLE test_view ADD CONSTRAINT isit CHECK ( field1 IS NOT NULL);
ALTER TABLE test_view ALTER field1 SET NOT NULL;

How can I do this?

Regards

Andreas
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Re: add constraints to views

From
Gaetano Mendola
Date:
Andreas Fromm wrote:

> CREATE VIEW test_view (
> ~    SELECT * FROM test_table WHERE tag
> );
>
> Now I want ad a NOT NULL constraint to the view on field1. I tryed the
> following, but neither works.

what does mean add a null constrain to a view ?  Do you mean
filter out the records with the field1 null ?

CREATE OR REPLACE test_view AS
     SELECT *
     FROM test_table
     WHERE field1 IS NOT NULL AND
           tag;


Regards
Gaetano Mendola

Re: add constraints to views

From
Andreas Fromm
Date:
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Gaetano Mendola wrote:
| Andreas Fromm wrote:
|
|> CREATE VIEW test_view (
|> ~    SELECT * FROM test_table WHERE tag
|> );
|>
|> Now I want ad a NOT NULL constraint to the view on field1. I tryed the
|> following, but neither works.
|
|
| what does mean add a null constrain to a view ?  Do you mean
| filter out the records with the field1 null ?
|
| CREATE OR REPLACE test_view AS
|     SELECT *
|     FROM test_table
|     WHERE field1 IS NOT NULL AND
|           tag;
|
No, I mean that the view behaves like a table with the same columns as
table, but that restricts to records on wich tag is set. To insert a
record to this "special"  table it requires to have field1 set. In other
words: A record of table is a record of view if tag is set. If tag is
set, then field1 has also have to have a value. If tag is not set, it
may have a value for field1, but will not show up in the view. Of course
I could achive this be triggers, but I thought it could be possible to
do via constraints on the view.

Regards

Andreas
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Re: add constraints to views

From
Tom Lane
Date:
Andreas Fromm <Andreas.Fromm@physik.uni-erlangen.de> writes:
> No, I mean that the view behaves like a table with the same columns as
> table, but that restricts to records on wich tag is set. To insert a
> record to this "special"  table it requires to have field1 set. In other
> words: A record of table is a record of view if tag is set. If tag is
> set, then field1 has also have to have a value. If tag is not set, it
> may have a value for field1, but will not show up in the view. Of course
> I could achive this be triggers, but I thought it could be possible to
> do via constraints on the view.

Constraints on a view are meaningless --- it has no real rows to
constrain.  Put the constraints on the underlying table.

            regards, tom lane