SEO

Folks,

please find attached a patch which implements psql command aliases. They
work the same way as on bash, zsh and others, for example:

#= \alias d \dt+
#= \d
List of relations
Schema | Name | Type | Owner | Description
--------+------+-------+-------+-------------
public | foo | table | bernd |
(1 row)

=# \alias current_query SELECT current_query, NOW() - query_start FROM
pg_stat_activity WHERE current_query NOT LIKE 'IDLE%';

#= \current_query
current_query
| ?column?
-------------------------------------------------------------------------------------------------------+----------
SELECT current_query, NOW() - query_start FROM pg_stat_activity WHERE
current_query NOT LIKE 'IDLE%'; | 00:00:00
(1 row)


#= \unalias d
#= \d
List of relations
Schema | Name | Type | Owner
--------+------+-------+-------
public | foo | table | bernd
(1 row)


I hope i broke nothing and maybe we find this useful for 8.4, documentation
included.

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Thanks

Bernd

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Bernd Helmle <mailings@oopsware.de> writes:
> please find attached a patch which implements psql command aliases. They
> work the same way as on bash, zsh and others, for example:

> #= \alias d \dt+
> #= \d

Do we really want such a thing? The space of backslash command names
is so densely populated already that it's hard to imagine creating
aliases without conflicting with existing (or future) command names
--- as indeed your example does. It seems like mostly a recipe for
confusion.

regards, tom lane

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Am Dienstag, 1. April 2008 schrieb Tom Lane:
> Do we really want such a thing?

Yes!

> The space of backslash command names
> is so densely populated already that it's hard to imagine creating
> aliases without conflicting with existing (or future) command names
> --- as indeed your example does. It seems like mostly a recipe for
> confusion.

This is a standard feature and effect on shells. Shells have even more likely
commands and conflicts, and still aliases are widely used. If people are
concerned about conflicts, they shouldn't use aliases.

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--On Dienstag, April 01, 2008 11:39:59 -0400 Tom Lane <tgl@sss.pgh.pa.us>
wrote:

> Do we really want such a thing?

Well, i use aliases everytime and everywhere they got implemented and i
found it quite useful to _extend_ existing behavior (integrating additional
functionality in an easy way)

> The space of backslash command names
> is so densely populated already that it's hard to imagine creating
> aliases without conflicting with existing (or future) command names

I often found existing backslash command sometimes overloaded or simply not
providing information i really need (for example, an easy way to get
information about current locales, encoding and user settings). You simply
can't catch all requirements DBA's and users want within a all-catching
implementation. Using this way, users are able to implement their own
command shortcuts

Overriding existing backslash commands (as my first example shows) is only
an implementation-specific detail which could easily forbidden. However,
defining your own shortcuts for your psql-sessions looks quite useful to
me, like my 2nd example tries to illustrate.

> It seems like mostly a recipe for confusion.

So what? This could happen in every shell that supports aliases as well. I
don't get your point...?

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Bernd

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"Peter Eisentraut" <peter_e@gmx.net> writes:

> Am Dienstag, 1. April 2008 schrieb Tom Lane:
>> Do we really want such a thing?
>
> Yes!
>
>> The space of backslash command names
>> is so densely populated already that it's hard to imagine creating
>> aliases without conflicting with existing (or future) command names
>> --- as indeed your example does. It seems like mostly a recipe for
>> confusion.
>
> This is a standard feature and effect on shells. Shells have even more likely
> commands and conflicts, and still aliases are widely used. If people are
> concerned about conflicts, they shouldn't use aliases.

I think you're crazy to think shells are more likely to have conflicts. Shells
require a whole token match, not just the first letter.

In other words, any alias *starting with* the letters c, d, e, f, g, h, i,
o, s, w, z would be a conflict. Just for maximum confusion the list of letters
which cause conflicts when capitalized would be entirely different.

Picture a newbie typoing on their \old alias and trying to figure out where
all their data is going... Hopefully they weren't too attached to whatever was
in their "ldd" file yesterday.

I could see it being handy being able to save commonly executed queries and
access them with a shortcut but I think you need to use a separate namespace
from psql's backslash commands. Perhaps `query` or invent a single backslash
command to execute them like "\query current_query". Actually I like that last
idea the most.

One thing to think about is how to pass arguments to the aliases. Csh put us
in the soup by hacking in arguments in a terrible way. As a result quoting in
csh aliases is awful. Even if it's not implemented right away I think we
should figure out what the syntax would be for passing arguments to be
interpolated into the query before backing ourselves into a corner.

I can't imagine much of a use case for being able to alias backslash commands
themselves. They're already ridiculously terse anyways. How many keystrokes
can you possibly save?

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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--On Donnerstag, April 03, 2008 03:13:47 +0100 Gregory Stark
<stark@enterprisedb.com> wrote:

> I think you're crazy to think shells are more likely to have conflicts.
> Shells require a whole token match, not just the first letter.
>
> In other words, any alias *starting with* the letters c, d, e, f, g, h, i,
> o, s, w, z would be a conflict. Just for maximum confusion the list of
> letters which cause conflicts when capitalized would be entirely
> different.
>
> Picture a newbie typoing on their \old alias and trying to figure out
> where all their data is going... Hopefully they weren't too attached to
> whatever was in their "ldd" file yesterday.

Of course, the patch doesn't work this way. Only complete tokens delivered
by the parser are substituted, illustrated here with your example:


#= \alias old SELECT version();
#= \old
version
---------------------------------------------------------------------------------------------------
PostgreSQL 8.4devel on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
4.2.3 (Debian 4.2.3-2)
(1 row)

#= \o foo
#= \old
#=
zsh: suspended psql
% cat foo
version
---------------------------------------------------------------------------------------------------
PostgreSQL 8.4devel on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
4.2.3 (Debian 4.2.3-2)
(1 row)

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Bernd

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"Bernd Helmle" <mailings@oopsware.de> writes:

>> Picture a newbie typoing on their \old alias and trying to figure out
>> where all their data is going... Hopefully they weren't too attached to
>> whatever was in their "ldd" file yesterday.
>
> Of course, the patch doesn't work this way. Only complete tokens delivered by
> the parser are substituted, illustrated here with your example:

To be more explicit what I meant was someone doing

#= \alias old select version();
....
#= \oldd
<oops>
#= \old
#= select 'where is all my output going?'
#= select 'what happened to my ldd file?'




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Am Donnerstag, 3. April 2008 schrieb Gregory Stark:
> To be more explicit what I meant was someone doing
>
> #= \alias old select version();
> ...
> #= \oldd
> <oops>
> #= \old
> #= select 'where is all my output going?'
> #= select 'what happened to my ldd file?'

This is a valid concern, but it is orthogonal to the alias feature. You have
the same problem already if you mistype

\oo instead of \o
\ofoo instead of \obar
\o instead of \p
\oset instead of \pset

or even more amusingly

\o foo instead of \i foo -- check your keyboard layout

and so on.

If you want to guard against typos, you need to remove the \o command in its
current form. Prohibiting the addition of new commands, by whichever means,
is not going to help. And we have never had a policy or real analysis
whether new or existing commands are typo-proof.

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"Peter Eisentraut" <peter_e@gmx.net> writes:

> This is a valid concern, but it is orthogonal to the alias feature. You have
> the same problem already if you mistype
>
> \oo instead of \o
> \ofoo instead of \obar

Not really. In these cases you know what \o is going to do, you've just typo'd
the filename. The case I was saying was a "conflict" was because you were
using an entirely different feature and might not never have even met \o.

> \o instead of \p
> \oset instead of \pset

Sure, if you typo \o instead of select * from pg_class you might be surprised
too. You can't protect against typing an entirely different command than
intended. At least you can then go look up what \o does and figure out what
happened.

If you type \ofoo instead of \obar I think there's a big difference between
having it accidentally do what you wanted it to do but to the wrong file and
having it do something entirely unrelated to what you intended and end up
overwriting a file instead of run a simple select.

> or even more amusingly
>
> \o foo instead of \i foo -- check your keyboard layout

The point is here you've typed a different command entirely. Unsurprisingly
it's going to do something different.

\old means something *today*. In the proposed syntax by creating the alias
you're changing what it means. You're not changing other \ofoo arguments
though which is where the possibility for confusion arises.

Consider instead if Debian decided to include a convenient \deb alias for a
select query against the package repository. Now if I happen to have an "eb"
table I will be surprised when \deb doesn't work.

And lengthening the alias doesn't really help (aside from defeating the
purpose of having aliases). If they define \debian they would still be
interfering if I should have a table named "ebian".

As rule of thumb, I think if you try to execute an alias which doesn't exist,
you should get an "alias does not exist" command. You should not get an
"Invalid command" nor "Did not find relation" and certainly not some random
command you've never met before being run reading or overwriting random files.


I repeat my suggestion of having a \query command so you could do:

\setquery deb select * from debian_packages where packagename like :1
\setquery bbdb select * from bbdb where name like :1

\query deb postgres
\query bbdb peter

to run a saved query. I'm not attached to "setquery" though.

--
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Am Donnerstag, 3. April 2008 schrieb Gregory Stark:
> \old means something *today*. In the proposed syntax by creating the alias
> you're changing what it means.

Yes. There are two complementary responses to that:

1. That's an intentional, useful feature of aliases.
2. If you don't like it, don't use it.

By your line of argument, we couldn't ever add any new commands in psql
anyway.

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