On Fri, Dec 14, 2012 at 7:22 AM, John R Pierce <pierce@hogranch.com> wrote:
> On 12/13/2012 5:32 AM, seiliki@so-net.net.tw wrote:
>>
>> I am trying to implement a mechanism that prohibits the last row of a data
>> set from being deleted.
>>
>> CREATE TABLE t1 (c1 INTEGER,c2 INTEGER, PRIMARY KEY (c1,c2));
>>
>> INSERT INTO t1 VALUES (1,1),(1,2),(1,3),(2,1),(2,2),(2,3);
>
>
> Which row is the last row? relations are sets, not ordered lists.
My understanding of the OP is that this is a constraint whereby there
must always be at least one remaining row for a given value of c1.
That is to say, you may delete any row from t1 as long as it's not the
last row (temporally, not sequentially) with that c1.
ChrisA