Subject: Re: [HACKERS] generated columns
To: Robert Haas <robertmhaas@gmail.com>
References: <b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com>
 <CAJGNTeOxeQPFpEr35PME4yLayRzP_wwzt70kFrPztSTWHf-HDA@mail.gmail.com>
 <CAJGNTeM+MCjA4dBhAdjJ-vR_CwY3u65cCcc+KvnahzLHZjxjbw@mail.gmail.com>
 <1bc948f8-3bab-6c54-50af-c0723a75b85f@2ndquadrant.com>
 <20180116063546.GA3679@paquier.xyz>
 <48502d9b-60c4-5b10-40a2-e34f562132b4@2ndquadrant.com>
 <20180119051804.GC12826@paquier.xyz>
 <2e3d5147-16f8-af0f-00ab-4c72cafc896f@2ndquadrant.com>
 <20180131131804.GB1586@paquier.xyz>
 <bf9c8765-1aa0-432a-442e-45f715ebe4e7@2ndquadrant.com>
 <20180202022532.GA84623@paquier.xyz>
 <050e663d-d915-f61b-af96-5a09c10ade02@2ndquadrant.com>
 <79e4de23-52e3-2c45-9ba0-5f6932f590aa@2ndquadrant.com>
 <CA+TgmoZ=LWpzn0S2NXBJhL+y8Bq1pF8gjrusTHF2acDjcnTb9w@mail.gmail.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
 Michael Paquier <michael.paquier@gmail.com>,
 Jaime Casanova <jaime.casanova@2ndquadrant.com>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Openpgp: preference=signencrypt
Autocrypt: addr=peter.eisentraut@2ndquadrant.com; prefer-encrypt=mutual;
 keydata=
 xsFNBFUUt6kBEADZd9NNTBJbHmAXXJgPGOdd6Q73l80oifIVgn2tRxP9dYkCfTlo/yLqbKTl
 JNqTcyM6XrJDnB2sMEUGYCewYZXl+9C4bBJWyNqcEI1ae9u71vEq/fknFLArJ+2wN+f7QuRx
 Q8d94ZJAiJQ5g3fNk2HVeedCQCKP5dCzU+ZLt2dbsx1PDZLjTO9gf+JswWuGFb5wY5PZVM5V
 hq66Xk7ZJzHuARacza2RT7J2fkMmQBY+kr7L98Perb0GhafnlhXB0PvUB+N3xpmggMfwuhTu
 BngS/G/r3GvemxJuFxouw8xsMqrsfdksJXA2gLXYtwRCssdPV3PO0rlD9twqDo8URfIJ5fb6
 1g/MV8aTOKjg3Q8MpJPtkwJqN4o3PvbwYdedeFnOVkkYAJdu/aX1v1BeCBDu7Hy3sF52scD3
 pQbyQSl9vUDpTLarASAxNbAV0NRJE8dp4vfW6AH1ccryGiFqw/czPK/iN0+MT8wsjAW6WW4w
 hvjm5UPA1KTwi3ZT8eT5uycuH7QpuNk7LnGGXQ6KaRALFywzkr0A0V0AvFNa+l4wstMaXaB6
 dmMXyF0/hfryqyOeu1gAdq4q0/PNC2dPgb/6uoh4eMjN6A5GXcprilhz5DulmsilY21hfSoU
 S64ODed96pKhprsOxjZiDRsN1QM5MwB+uwVWUNfsX7fIxE0BrwARAQABzSdQZXRlciBFaXNl
 bnRyYXV0IDxwZXRlckBlaXNlbnRyYXV0Lm9yZz7CwXoEEwEIACQCGwMFCwkIBwMFFQoJCAsF
 FgIDAQACHgECF4AFAlUUuKQCGQEACgkQoZ8SQ+xBJp8llw//RbGoXnF72FZTlOFsnNyxnWbF
 vViPCfdAlZl1GGK9OYCvV1dp/956HuhB0wpaGQHiBmQfOPJf/jLOPjXFYm2iEChEycrBChuE
 j4TSYemMp5BSPILYk9Uwd16kVD/+U6fQfK6H5pOhfBvbM6asMnmpY2wQuvktxHvaGlytFw84
 EzFWNZtAZfxkw28w3AhIQkKe9hJanfyDL750RcbyEr8AAHty5IErrvS7tM5vQwIeh5BF26ND
 CyKPRdZgOgMpcwFfROKBDpAt052CgWIpNdhBdfIKlkCs4/ILxmC3rT/Mb/qZiHcoMMwEu6k+
 T7vRAFZZAk62Yrr/U8/vUGKlzRZQoo86fyojCfI0ibCIc0z8rwCVY9P40G9wD9BTCZS/z8Vh
 jjpBlNnIKw2hM6hbxavKndCJjFFJD08rXrTyrLF/of18xD37vNdYooP9VATB5QjOWFRrscSZ
 4a89e+to3m7YVnd4xdXwGp47dYusoax84C8tg1gZrH38ol9dPmnKX6GZrXeS7tH9k8VeUpJ8
 HQbRThQRWAT936QpYbLConBmOtmbLmjQOGtiXPo1oK57X/7U/WBja5vWmm2q+Yxtt+3uHGVg
 DdDU4CJpXo4lX0v2n3QV5EBSW9hjdF3bNfl6GFBb1pPEhqNcMDUc7zkx/2uENdAdk/BnqMgH
 umip7b0pVfvOwU0EVRS3qQEQAJf6p0P7D+hMYUgCPkvgrcz6OJYsAYdUMUmokfqmkKwK0oJM
 ew8TNGM53ocKAgQGma5f10rwbZNPlpVPNRX5hwUmwVlcwSut0oE+JfUBH7mpysWvpF05RKIy
 q9RCoJZrAbXS7Tig56A1QD8IcM00rERZMcCOlI1+q9m4u9AOI+0LyGGSH+VvoyDHD/Jew4R2
 TmPEF8Pu7lYiNYK88Q6u0kBkc+Tz3BNlyc6fi3HxnFfp0b75HLXPSTu2SwA/0Q31wHZXwrEU
 BR9KgSn/qbgy8ydPc97i82fhiFE3cbGexfPrQSMYmDGi+dcQ0s+AMQwC3XyMC0JkHpYUuFkR
 QdlIvaIhgFUUN2Vr4xF2ADaNTNFc4DYaiPHFAgHZw+3pZWqS4uIiWgJynrEaHw4F3QWU8/JB
 iyEWDhNq4WBrRA0u914TCCAoFOOKMnRdl8eJrRQKM/5/lXbHFjjlI/LDKhLRFsuQsnJJ3331
 RjCzpHPZG5/p5KR1RHiAXa0p/DW5lXyq21hS3kjDlleoHqOxCN/cy0Jgz7qLDq1vZoCl67Sy
 RAH60c2Xu4may9SVltmot0OzWVHdrfS+85FQGp9580DaeLio7YMFKy2bfEvwQJ/c9xD2QPB+
 oSb3V8ueSznXBG5+dyfOsZFRPxceA0wA2rSWZSjxLdKxvyGTj9vsCjaDu13rABEBAAHCwV8E
 GAEIAAkFAlUUt6kCGwwACgkQoZ8SQ+xBJp+HJhAAxmSTsC5y7p9Zu+nnLpucv/h88oEx985e
 qWeXzQiwM3pfRZS+PdTH9TyzHK0KOgKoAiubk0vt+BrT91D9d0G5kVQaTctAErGBoMkTaZJT
 XVEcNphiPzysdSqvprjojMp1y7rG8AP+Xd6m0rE1LRnkRRm8HyI8vdXsuLQPITGWXDLMjaNq
 AOV3BUnzkgtjMuIYw7SCr+12ZOb5dEKvaG4kjC4kaJ/TLbuBhVANcXkC90yp0AOZLs/cB1Dj
 OAXno/RUUruJ3r27a+pFv768UAi9QWcdw58yPxreMNMLqAgsS9oTHwHfGNWcB2dJ4UW+GMLJ
 hTf9TjQ2f+N/sIx5XMQ9pYw6CAJMK29qPx6/ZayrPxf22EXf0D3zTwIEZgwfSkynFVwV25L7
 awQq60fifdMYheSxq7GbhpsixmcD+e161cCmLIt75YDt5bQ0B1yf7EmxG8n7pGZAOM6LoNsU
 fkSldba5XVwh8LuN5mK0nQBELGW6Os4TDq4REggLpfcvFC215zpuo0iCGnmE/Bns4nowqUSP
 u4tkWL+nxW4qgv8wo8HJ52jd79EJ8iqfIBoidBfy9AIUiEUApGQzWPu6yWcI8fY0rN5D+tc+
 Yw1Zt6Mm+huYJpgCRsTcfzEcahnBn521CWcWvhW1ff3KFileFMtNmnBBhMncmRKHphtTKEpN
 3jI=
Organization: 2ndQuadrant
Message-ID: <af76601d-5483-d718-dda4-6222080caa21@2ndquadrant.com>
Date: Thu, 22 Nov 2018 16:16:34 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0)
 Gecko/20100101 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: 
 <CA+TgmoZ=LWpzn0S2NXBJhL+y8Bq1pF8gjrusTHF2acDjcnTb9w@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 15/11/2018 15:10, Robert Haas wrote:
> I don't have a strong position on 1 vs. 2 vs. 3, but I do think it
> would be nicer not to use '\0' as a column value.  I'd suggest you use
> 'n' or '0' or '-' or some other printable character instead.

I had carefully considered this when attidentity was added.  Using '\0'
allows you to use this column as a boolean in C code, which is often
convenient.  Also, there are numerous places where a pg_attribute form
or a tuple descriptor is initialized to all zeroes, which works well for
most fields, and adding one exception like this would create a lot of
extra work and bloat the patch and create potential for future
instability.  Also note that a C char '\0' is represented as '' (empty
string) in SQL, so this also creates a natural representation in SQL.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services