| From: | Richard Huxton <dev(at)archonet(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>, pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: Can't ri_KeysEqual() consider two nulls as equal? |
| Date: | 2007-04-18 08:11:57 |
| Message-ID: | 4625D2CD.1030200@archonet.com |
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| Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Tue, 2007-04-17 at 17:16 -0400, Tom Lane wrote:
>> A recent discussion led me to the idea that FK triggers are fired
>> unnecessarily during an UPDATE if the foreign-key column(s) contain
>> any NULLs, because ri_KeysEqual() treats two nulls as unequal,
>> and therefore we conclude the row has changed when it has not.
>
> FK trigger *can be optimised away* is true. No need to have a discussion
> about whether NULL == NULL, but the critical test is: if I overwrote it,
> would you be able to tell? The answer is No, so away it goes.
The test should perhaps be named "unchanged" rather than "equal".
--
Richard Huxton
Archonet Ltd
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