From: | Chris Angelico <rosuav(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: How to keep the last row of a data set? |
Date: | 2012-12-13 21:15:15 |
Message-ID: | CAPTjJmoyjcJnPB74ucgp5hb=Qv+kwgiq6ZSjvGXMOsnV_RCjGQ@mail.gmail.com |
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Lists: | pgsql-general |
On Fri, Dec 14, 2012 at 7:22 AM, John R Pierce <pierce(at)hogranch(dot)com> wrote:
> On 12/13/2012 5:32 AM, seiliki(at)so-net(dot)net(dot)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
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