Обсуждение: SQL CONSTRAINTS - Constraining time values from two attributes on a table.

Hi,
I was looking for a solution on how to write a constraint into a ' create
table ' expression that would ensure that one ' TIME ' attribute value
called arrival_time (declared as TIME) is allways constrained to have a
value that ensures it is allways after another attribute value called
departure_time (declared as TIME). 
Any know how this constraint would be written??

Any help on this would be much appreciated,
Thanks,
Chris.

Chris,

> Hi,
> I was looking for a solution on how to write a constraint into a '
> create
> table ' expression that would ensure that one ' TIME ' attribute
> value
> called arrival_time (declared as TIME) is allways constrained to have
> a
> value that ensures it is allways after another attribute value called
> departure_time (declared as TIME).
> Any know how this constraint would be written??

Easy:

CONSTRAINT arr_dep_time CHECK ( arrival_time > departure_time )

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Maher, Christopher W writes:

> I was looking for a solution on how to write a constraint into a ' create
> table ' expression that would ensure that one ' TIME ' attribute value
> called arrival_time (declared as TIME) is allways constrained to have a
> value that ensures it is allways after another attribute value called
> departure_time (declared as TIME).

create table test (   arrival_time time,   departure_time time,   check (arrival_time < departure_time)
);

insert into test values ('12:00', '14:30');
INSERT 20651 1

insert into test values ('12:00', '9:45');
ERROR:  ExecAppend: rejected due to CHECK constraint $1

-- 
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter

> I was looking for a solution on how to write a constraint into a ' create
> table ' expression that would ensure that one ' TIME ' attribute value
> called arrival_time (declared as TIME) is allways constrained to have a
> value that ensures it is allways after another attribute value called
> departure_time (declared as TIME). 
> Any know how this constraint would be written??
> 

CREATE TABLE tablename (arrival_time        timestamp,departure_time        timestamp CHECK (arrival_time <
departure_time)
);