From: Phil Endecott <spam_from_postgresql_sql@chezphil.org>
To: Kenneth Gonsalves <lawgon@thenilgiris.com>
To: pgsql-sql@postgresql.org
Subject: Re: finding if a foreign key is in use
Date: Thu, 01 Jul 2004 10:57:23 +0100
Message-ID: <40E3E003.4050405@chezphil.org> (raw)
In-Reply-To: <0407010743031D.02481@thenilgiris.com>
References: <0406290618410W.02481@thenilgiris.com>
<7679232@chezphil.org>
<0407010743031D.02481@thenilgiris.com>
>>>in my app i have a table where the id serves as a foreign key for
>>>one or more other tables. if i want to delete a row in the table,
>>>i currently search the other tables where this table is referenced
>>>to see if the row is in use - and then, if not in use, permit
>>>deletion.
>>>Now if i want the delete button in my app to be disabled whenever
>>>a row that is in use is selected, searching the database every time
>>>would dramatically slow down the app.
>>
>>Basically you do have to do this search. But it won't be too slow if you
>>create an index on the foreign key.
>
> pity. thought postgres would have some function like 'in_use' to tell when a
> row that is used as a foreign key is in actual use and hence cannot be
> deleted. surely, in a database of millions of records, it wouldnt have search
> them all to find if the row is in use?
It doesn't "search them all" if you have an index. If your database has
a million records it needs to look at only 20 index entries, as 2^20 is
about a million. (At least that's what I, naively, think it should do -
anyone who knows more want to correct me?)
--Phil.
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: spam_from_postgresql_sql@chezphil.org, lawgon@thenilgiris.com
Subject: Re: finding if a foreign key is in use
In-Reply-To: <40E3E003.4050405@chezphil.org>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox