PostgreSQL metacommands
lazarus / 16-Databases

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Elmug · 2012-06-21 11:42

Hi everyone,

If anyone knows how to send meta-commands to the PostgreSQL engine,
from a Lazarus application, I would appreciate some guidance.

Thanks!

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goodname · 2012-06-21 12:57

I'm guessing that meta commands means "alter" or other commands that
do not have to due with data manipulation. Just use ExecSQL or
ExecuteDirect.

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Elmug · 2012-06-21 14:01

Quote from: goodname on June 21, 2012, 02:57:02 pmI'm guessing that
meta commands means "alter" or other commands that do not have to due
with data manipulation. Just use ExecSQL or ExecuteDirect.

goodname, the metacommands start with the backslash (\) and they are
not quite the same as "queries".

I will check on what you say, though.

Thanks.

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BigChimp · 2012-06-21 14:09

I think he means this:
http://www.postgresql.org/docs/current/static/app-psql.html
QuoteAnything you enter in psql that begins with an unquoted backslash
is a psql meta-command that is processed by psql itself.
Edit:In other words, the postgresql server never even receives these
"commands"; they're specific to the command line psql program.

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Elmug · 2012-06-21 14:26

Quote from: BigChimp on June 21, 2012, 04:09:29 pmI think he means
this:
http://www.postgresql.org/docs/current/static/app-psql.html
QuoteAnything you enter in psql that begins with an unquoted backslash
is a psql meta-command that is processed by psql itself.
In other words, the postgresql server never even receives these
"commands"; they're specific to the command line psql program.

BigChimp,

Some commands do reach the server.

For instance:
\password [ username ]

    Changes the password of the specified user (by default, the
current user). This command prompts for the new password, encrypts it,
and sends it to the server as an ALTER ROLE command. This makes sure
that the new password does not appear in cleartext in the command
history, the server log, or elsewhere.


There are others.

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BigChimp · 2012-06-21 14:27

Thanks for the correction Elmug, you're right

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goodname · 2012-06-21 14:50

Even in the case of the psql \password meta command it looks like psql
client is doing a lot of work to prepare the "alter" command. I can
see how using psql \password would be useful and would be interested
in seeing your solution if you find one.

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Elmug · 2012-06-21 15:35

Quote from: goodname on June 21, 2012, 04:50:04 pmEven in the case of
the psql \password meta command it looks like psql client is doing a
lot of work to prepare the "alter" command. I can see how using psql
\password would be useful and would be interested in seeing your
solution if you find one.

Hi goodname, and other helpers,

I am working on this approach right now:

1. At Lazarus application, have a box to specify PARAMETERS.
2. Using the PROCESS unit, create a PROCESSpgSQL:=TProcess;
3. TProcess:='pgSQL.exe PARAMETERS'..... Also, with path to wherever
pgSQL.exe is located, of course (or copy it to folder with resultant 
lazarus application )

Here, PARAMETERS means whatever it takes to start pgSQL as needed,
including the redirection of its ouput to pgOutput.txt.

This way, I believe I will also solve the capability of sending BOTH
QUERIES that can be audited BEFORE sending, and also have the
capability to send META-COMMANDS, and to read pgOutput.txt in a second
memobox.

So there will actually be 3 boxes used. One for parameters, one for
the input query (which can now send metacommands), and one memo box to
put the contents of the pgOutput.txt.

Right now, I don't see why it wouldn't work. All this remains client-
based.

NOTE: PARAMETERS will also include whatever it takes to run pgSQL.exe
in silent mode, meaning that the application user will NEVER see the
pgSQL shell screen.

Please let me know of opinion/corrections.

Thanks.