On 30/1/20 6:49 μ.μ., Adrian Klaver wrote:
On 1/30/20 3:46 AM, Achilleas Mantzios wrote:
On 29/1/20 8:32 μ.μ., Adrian Klaver wrote:
On 1/29/20 8:12 AM, Achilleas Mantzios wrote:
Hello Dear Postgresql ppl,
I have a table with date ranges and need to express the following constraint :
allow overlaps only if there is complete containment, e.g.
allow values in rows like :
[2020-01-01,2020-01-31)
[2020-01-02,2020-01-10)
[2020-01-10,2020-01-20)
but disallow rows like
[2020-01-02,2020-01-10)
[2020-01-08,2020-01-11)
I'm missing something. Can you provide a more complete example?
Dear Adrian,
I can give an example, lets say that we want to model the concept of budget, and we allow basic complete budgets covering a specific time period (daterange) which will have predictions and also
matched actual transactions (Debits, Credits) , but also want "super" budgets of larger time periods which include a number of basic budgets (sub-budgets) and for which only predictions are
allowed, not actual transactions. We could make the design strict and explicit by using referential constraints (basic budget pointing to a super budget) but If we chose to not make it strict , and
conversely allow a more dynamic and liberal way that the system detects one form or the other , we could say :
each sub-budget (of the lowest level of the hierarchy - although for the time
being we have only two levels) cannot overlap with any other sub-budget
each super-budget can only fully contain its sub-budgets , no partial overlap
allowed.
Um, that makes my head hurt:) Questions:
1) Are the basic complete budgets and the sub-budgets and super budgets
existing in the same table?
2) Depending on answer to 1, to prevent overlap could you not use a form of the
example here?:
https://www.postgresql.org/docs/12/rangetypes.html#RANGETYPES-CONSTRAINT
CREATE TABLE reservation (
during tsrange,
EXCLUDE USING GIST (during WITH &&)
);
same table.
overlap is allowed but only when it is complete containment, which is the whole
point of this thread.
This could be solved easily if there was a commutative containment operator
like :
CREATE OR REPLACE FUNCTION range_containment(anyrange, anyrange)
RETURNS boolean
LANGUAGE sql
IMMUTABLE PARALLEL SAFE STRICT
AS $function$
select $1 <@ $2 OR $1 @> $2;
$function$;
so range_containment returns true if the first operand is contained in the
second or contains the second.
create operator <@@> (PROCEDURE=range_containment, LEFTARG=anyrange,
RIGHTARG=anyrange, COMMUTATOR = <@@> );
But unfortunately :
alter table bdynacom.acc_budget ADD CONSTRAINT acc_budget_start_end EXCLUDE USING
gist (daterange(period_start, period_end, '[]'::text) WITH <@@>);
ERROR: operator <@@>(anyrange,anyrange) is not a member of operator family
"range_ops"
DETAIL: The exclusion operator must be related to the index operator class for
the constraint.
From a small research I did this might mean recompiling the source to make
<@@> member of range_ops .
I think that writing a new commutative range operator e.g. |<@@> which would return true if the left operand is either contained by or contains the right operand and false otherwise would solve
this, I am just wondering if there is a more elegant and economical way to express this. (besides writing a trigger which is always an option).|
--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt
--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt
