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-From tgl@sss.pgh.pa.us Wed Nov 21 22:51:02 2001
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-To: Bruce Momjian <pgman@candle.pha.pa.us>
-cc: Peter Eisentraut <peter_e@gmx.net>,
- PostgreSQL Development <pgsql-hackers@postgresql.org>,
- stiening@cannon.astro.umass.edu, pgsql-bugs@postgresql.org
-Subject: Re: [BUGS] Bug #513: union all changes char(3) column definition
-In-Reply-To: <200111220310.fAM3A2V08766@candle.pha.pa.us>
-References: <200111220310.fAM3A2V08766@candle.pha.pa.us>
-Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
- message dated "Wed, 21 Nov 2001 22:10:02 -0500"
-Date: Wed, 21 Nov 2001 22:51:04 -0500
-Message-ID: <27975.1006401064@sss.pgh.pa.us>
-From: Tom Lane <tgl@sss.pgh.pa.us>
-Status: ORr
-
-Bruce Momjian <pgman@candle.pha.pa.us> writes:
-> Added to TODO:
-> * CREATE TABLE AS can not determine column lengths from expressions
-> Seems it should be documented. Do we throw an error in these cases?
-
-No. What we do right now is to generate non-length-constrained column
-types for the created table.
-
-Your TODO item is too pessimistic: we *do* determine the column length
-in simple cases. For example:
-
-regression=# create table foo (f1 char(3));
-CREATE
-regression=# create table bar as select * from foo;
-SELECT
-regression=# \d bar
- Table "bar"
- Column | Type | Modifiers
---------+--------------+-----------
- f1 | character(3) |
-
-However, in more complex cases we don't know the column length:
-
-regression=# create table baz as select f1 || 'z' as f1 from foo;
-SELECT
-regression=# \d baz
- Table "baz"
- Column | Type | Modifiers
---------+--------+-----------
- f1 | bpchar |
-
-The argument here is about how much intelligence it's reasonable to
-expect the system to have. It's very clearly not feasible to derive
-a length limit automagically in every case. How hard should we try?
-
- regards, tom lane
-
-From pgsql-bugs-owner+M2695=candle.pha.pa.us=pgman@postgresql.org Wed Nov 21 23:16:19 2001
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-To: Bruce Momjian <pgman@candle.pha.pa.us>
-cc: Peter Eisentraut <peter_e@gmx.net>,
- PostgreSQL Development <pgsql-hackers@postgresql.org>,
- stiening@cannon.astro.umass.edu, pgsql-bugs@postgresql.org
-Subject: Re: [BUGS] Bug #513: union all changes char(3) column definition
-In-Reply-To: <200111220353.fAM3rRg12994@candle.pha.pa.us>
-References: <200111220353.fAM3rRg12994@candle.pha.pa.us>
-Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
- message dated "Wed, 21 Nov 2001 22:53:27 -0500"
-Date: Wed, 21 Nov 2001 23:08:37 -0500
-Message-ID: <28079.1006402117@sss.pgh.pa.us>
-From: Tom Lane <tgl@sss.pgh.pa.us>
-Precedence: bulk
-Sender: pgsql-bugs-owner@postgresql.org
-Status: OR
-
-Bruce Momjian <pgman@candle.pha.pa.us> writes:
-> However, I don't think creating a bpchar
-> with no length is a proper solution. Should we just punt to text in
-> these cases?
-
-How many special cases like that do you want to put into the allegedly
-datatype-independent CREATE TABLE code?
-
-If I thought this were the only case then I'd not object ... but it
-looks like a slippery slope from here.
-
-And --- it's not like replacing "bpchar" with "text" actually buys us
-any useful new functionality. AFAICS it's just a cosmetic thing.
-
- regards, tom lane
-
-PS: On the other hand, we might consider attacking the problem from
-the reverse direction, ie *removing* code. For example, if there
-weren't redundant || operators for char and varchar, then every ||
-operation would yield text, and the example we're looking at would
-work the way you want for free. I've thought for awhile that we
-could use a pass through pg_proc and pg_operator to remove some
-entries we don't really need.
-
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-From tgl@sss.pgh.pa.us Wed Nov 21 23:08:36 2001
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- Wed, 21 Nov 2001 23:08:37 -0500 (EST)
-To: Bruce Momjian <pgman@candle.pha.pa.us>
-cc: Peter Eisentraut <peter_e@gmx.net>,
- PostgreSQL Development <pgsql-hackers@postgresql.org>,
- stiening@cannon.astro.umass.edu, pgsql-bugs@postgresql.org
-Subject: Re: [BUGS] Bug #513: union all changes char(3) column definition
-In-Reply-To: <200111220353.fAM3rRg12994@candle.pha.pa.us>
-References: <200111220353.fAM3rRg12994@candle.pha.pa.us>
-Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
- message dated "Wed, 21 Nov 2001 22:53:27 -0500"
-Date: Wed, 21 Nov 2001 23:08:37 -0500
-Message-ID: <28079.1006402117@sss.pgh.pa.us>
-From: Tom Lane <tgl@sss.pgh.pa.us>
-Status: ORr
-
-Bruce Momjian <pgman@candle.pha.pa.us> writes:
-> However, I don't think creating a bpchar
-> with no length is a proper solution. Should we just punt to text in
-> these cases?
-
-How many special cases like that do you want to put into the allegedly
-datatype-independent CREATE TABLE code?
-
-If I thought this were the only case then I'd not object ... but it
-looks like a slippery slope from here.
-
-And --- it's not like replacing "bpchar" with "text" actually buys us
-any useful new functionality. AFAICS it's just a cosmetic thing.
-
- regards, tom lane
-
-PS: On the other hand, we might consider attacking the problem from
-the reverse direction, ie *removing* code. For example, if there
-weren't redundant || operators for char and varchar, then every ||
-operation would yield text, and the example we're looking at would
-work the way you want for free. I've thought for awhile that we
-could use a pass through pg_proc and pg_operator to remove some
-entries we don't really need.
-
-From pgsql-bugs-owner+M2696=candle.pha.pa.us=pgman@postgresql.org Wed Nov 21 23:26:07 2001
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-From: Bruce Momjian <pgman@candle.pha.pa.us>
-Message-ID: <200111220413.fAM4DSH15042@candle.pha.pa.us>
-Subject: Re: [BUGS] Bug #513: union all changes char(3) column definition
-In-Reply-To: <28079.1006402117@sss.pgh.pa.us> "from Tom Lane at Nov 21, 2001
- 11:08:37 pm"
-To: Tom Lane <tgl@sss.pgh.pa.us>
-Date: Wed, 21 Nov 2001 23:13:28 -0500 (EST)
-cc: Peter Eisentraut <peter_e@gmx.net>,
- PostgreSQL Development <pgsql-hackers@postgresql.org>,
- stiening@cannon.astro.umass.edu, pgsql-bugs@postgresql.org
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-
-> How many special cases like that do you want to put into the allegedly
-> datatype-independent CREATE TABLE code?
->
-> If I thought this were the only case then I'd not object ... but it
-> looks like a slippery slope from here.
->
-> And --- it's not like replacing "bpchar" with "text" actually buys us
-> any useful new functionality. AFAICS it's just a cosmetic thing.
->
-> regards, tom lane
->
-> PS: On the other hand, we might consider attacking the problem from
-> the reverse direction, ie *removing* code. For example, if there
-> weren't redundant || operators for char and varchar, then every ||
-> operation would yield text, and the example we're looking at would
-> work the way you want for free. I've thought for awhile that we
-> could use a pass through pg_proc and pg_operator to remove some
-> entries we don't really need.
-
-Can we convert bpchar to text in create table if no typmod is supplied?
-
---
- Bruce Momjian | http://candle.pha.pa.us
- pgman@candle.pha.pa.us | (610) 853-3000
- + If your life is a hard drive, | 830 Blythe Avenue
- + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
-
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-From peter_e@gmx.net Thu Nov 22 12:14:01 2001
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-From: Peter Eisentraut <peter_e@gmx.net>
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-To: Tom Lane <tgl@sss.pgh.pa.us>
-cc: Bruce Momjian <pgman@candle.pha.pa.us>,
- PostgreSQL Development <pgsql-hackers@postgresql.org>
-Subject: Re: [BUGS] Bug #513: union all changes char(3) column definition
-In-Reply-To: <27975.1006401064@sss.pgh.pa.us>
-Message-ID: <Pine.LNX.4.30.0111221803230.766-100000@peter.localdomain>
-MIME-Version: 1.0
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-Status: OR
-
-Tom Lane writes:
-
-> The argument here is about how much intelligence it's reasonable to
-> expect the system to have. It's very clearly not feasible to derive
-> a length limit automagically in every case. How hard should we try?
-
-I would like to know what Proprietary database #1 does with
-
-CREATE TABLE one ( a bit(6) );
-INSERT INTO one VALUES ( b'101101' );
-CREATE TABLE two ( b bit(4) );
-INSERT INTO two VALUES ( b'0110' );
-CREATE TABLE three AS SELECT a FROM one UNION SELECT b FROM two;
-
-According to SQL92, clause 9.3, the result type of the union is bit(6).
-However, it's not possible to store a bit(4) value into a bit(6) field.
-Our current solution, "bit(<nothing>)" is even worse because it has no
-real semantics at all (but you can store bit(<anything>) in it,
-interestingly).
-
---
-Peter Eisentraut peter_e@gmx.net
-
-
projects / postgresql / commitdiff