On 9/1/23 11:30, Peter Eisentraut wrote:
1) If I write UNIQUE (a, b, c WITHOUT OVERLAPS), does the WITHOUT
OVERLAPS clause attach to the last column, or to the whole column list?
In the SQL standard, you can only have one period and it has to be
listed last, so this question does not arise. But here we are building
a more general facility to then build the SQL facility on top of. So I
think it doesn't make sense that the range column must be last or that
there can only be one. Also, your implementation requires at least one
non-overlaps column, which also seems like a confusing restriction.
I think the WITHOUT OVERLAPS clause should be per-column, so that
something like UNIQUE (a WITHOUT OVERLAPS, b, c WITHOUT OVERLAPS) would
be possible. Then the WITHOUT OVERLAPS clause would directly correspond
to the choice between equality or overlaps operator per column.
An alternative interpretation would be that WITHOUT OVERLAPS applies to
the whole column list, and we would take it to mean, for any range
column, use the overlaps operator, for any non-range column, use the
equals operator. But I think this would be confusing and would prevent
the case of using the equality operator for some ranges and the overlaps
operator for some other ranges in the same key.
I prefer the first option. That is: WITHOUT OVERLAPS applies only to
the column or expression it is attached to, and need not be last in line.
--
Vik Fearing
