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