Thread: Libpq coding assistance
I am in need of some assistance in coding a c module using libpq on a
windows platform. Specifically, I need some help with providing the
input buffer for lo_write. The code sample provided in the
documentation contains this snippet:
------------
lobj_fd = lo_open(conn, lobjId, INV_WRITE);
while ((nbytes = read(fd, buffer,BUFSIZE)) > 0)
{
tmp = lo_write(conn, lobj_fd, buffer, nbytes);
if (tmp < nbytes)
fprintf(stderr, "error while reading large object\n");
}
(void) CloseHandle(fd);
(void) lo_close(conn, lobj_fd);
------------
I need to change the read() statement to use ReadFile, thus:
------------
lobj_fd = lo_open(conn, lobjId, INV_WRITE);
while (ReadFile(fd, buffer, BUFSIZE, &nbytes, NULL)!=EOF )
{
tmp = lo_write(conn, lobj_fd, buffer, nbytes);
if (tmp < nbytes)
fprintf(stderr, "error while reading large object\n");
}
(void) lo_close(conn, lobj_fd);
(void) CloseHandle(fd);
--------------
This, of course, doesn't work. The program is reported as no longer responding.
An infinite loop I suspect. If anyone is doing this or knows how to code it,
I would be grateful.
--
---------------------------------------------------------------------
Scott Holmes http://pages.sbcglobal.net/scottholmes
scottholmes@sbcglobal.net
Independent Programmer/Analyst Passport 4GL
PHP HTML Composer PostgreSQL Informix 4GL, SQL
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There are more things in heaven and earth, Horatio,
than are dreamt of in your philosophy
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Hi, Is there an internal timestamp on a table when it was created? I want to the program to perform an auto daily backup on certain tables. If I can check time stamp on the table as when it was created, so I can set the program to do just one backup a day. Thanks -Jeff
Scott Holmes <scottholmes@sbcglobal.net> writes:
> ------------
>
> lobj_fd = lo_open(conn, lobjId, INV_WRITE);
>
> while ((nbytes = read(fd, buffer,BUFSIZE)) > 0)
> {
> }
>
> ------------
>
> I need to change the read() statement to use ReadFile, thus:
>
> ------------
> lobj_fd = lo_open(conn, lobjId, INV_WRITE);
>
> while (ReadFile(fd, buffer, BUFSIZE, &nbytes, NULL)!=EOF )
> {
> }
> --------------
>
> This, of course, doesn't work. The program is reported as no longer
> responding. An infinite loop I suspect. If anyone is doing this or
> knows how to code it, I would be grateful.
Sounds like ReadFile (a Windows call?) isn't behaving the way you
think it does. Write some test code and play around with it until you
understand how it works.
-Doug
--
Let us cross over the river, and rest under the shade of the trees.
--T. J. Jackson, 1863
Hi, I'm getting parser error at or near AS when try to copy a table using CREATE TABLE AS Here what I have in the sql statement CREATE TABLE employee_backup (id text UNIQUE, lastname text, firstname text, phone text) AS SELECT * FROM employee Can some body tell me what is wrong with the sql statement? Thank you
On Sun, 4 Nov 2001, Jeff Lu wrote: >Hi, >I'm getting parser error at or near AS >when try to copy a table using CREATE TABLE AS >Here what I have in the sql statement >CREATE TABLE employee_backup (id text UNIQUE, lastname text, firstname text, >phone text) AS SELECT * FROM employee >Can some body tell me what is wrong with the sql statement? I don't believe you can specify types or constraints. Also, if you specify the name of each column in parens, PostgreSQL seems to get confused if you do a SELECT * following AS, rather than specify each table name as well (as of 7.1.x, I get ERROR: CREATE TABLE/AS SELECT has mismatched column count - is this a known bug?) I believe this should work, though you lose the UNIQUE constraint: CREATE TABLE employee_backup AS SELECT * FROM employee; Regards, Jw. -- jlx@commandprompt.com by way of pgsql-general@commandprompt.com
On Sun, 4 Nov 2001, Command Prompt, Inc. wrote: >I don't believe you can specify types or constraints. Also, if you specify >the name of each column in parens, PostgreSQL seems to get confused if you >do a SELECT * following AS, rather than specify each table name as well >(as of 7.1.x, I get ERROR: CREATE TABLE/AS SELECT has mismatched column >count - is this a known bug?) Er, make that "column name" above, not "table name". Here's an example of what I was trying to describe: lx=# CREATE TABLE abc (a char, b char, c char); CREATE lx=# CREATE TABLE xyz (x, y, z) AS SELECT * FROM abc; ERROR: CREATE TABLE/AS SELECT has mismatched column count lx=# CREATE TABLE xyz (x, y, z) AS SELECT a, b, c FROM abc; SELECT You can explicitly provide each column name in the AS SELECT clause, and that appears to work properly, but supplying a "*" confuses the backend. Is this as it should be, or is it a known issue? Regards, Jw. -- jlx@commandprompt.com by way of pgsql-general@commandprompt.com
"Command Prompt, Inc." <pgsql-general@commandprompt.com> writes:
> lx=# CREATE TABLE abc (a char, b char, c char);
> CREATE
> lx=# CREATE TABLE xyz (x, y, z) AS SELECT * FROM abc;
> ERROR: CREATE TABLE/AS SELECT has mismatched column count
> lx=# CREATE TABLE xyz (x, y, z) AS SELECT a, b, c FROM abc;
> SELECT
Looks like a bug to me too. Will look into it.
regards, tom lane
Tom Lane <tgl@sss.pgh.pa.us> writes:
> "Command Prompt, Inc." <pgsql-general@commandprompt.com> writes:
>> lx=# CREATE TABLE abc (a char, b char, c char);
>> CREATE
>> lx=# CREATE TABLE xyz (x, y, z) AS SELECT * FROM abc;
>> ERROR: CREATE TABLE/AS SELECT has mismatched column count
>> lx=# CREATE TABLE xyz (x, y, z) AS SELECT a, b, c FROM abc;
>> SELECT
> Looks like a bug to me too. Will look into it.
Fix committed for 7.2.
regards, tom lane
Thanks,
will this be fixed on the next release?
-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org]On Behalf Of Tom Lane
Sent: Sunday, November 04, 2001 9:02 PM
To: Command Prompt, Inc.; Jeff Lu; Postgresql General
Subject: Re: [GENERAL] Got error on CREATE TABLE AS (+Bug?)
Tom Lane <tgl@sss.pgh.pa.us> writes:
> "Command Prompt, Inc." <pgsql-general@commandprompt.com> writes:
>> lx=# CREATE TABLE abc (a char, b char, c char);
>> CREATE
>> lx=# CREATE TABLE xyz (x, y, z) AS SELECT * FROM abc;
>> ERROR: CREATE TABLE/AS SELECT has mismatched column count
>> lx=# CREATE TABLE xyz (x, y, z) AS SELECT a, b, c FROM abc;
>> SELECT
> Looks like a bug to me too. Will look into it.
Fix committed for 7.2.
regards, tom lane
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Yes, I've tried the following and it worked but the unique key contraint is losed. CREATE TABLE employee_backup AS SELECT * FROM employee; -----Original Message----- From: Command Prompt, Inc. [mailto:pgsql-general@commandprompt.com] Sent: Sunday, November 04, 2001 3:31 PM To: Jeff Lu Cc: Postgresql General Subject: Re: [GENERAL] Got error on CREATE TABLE AS (+Bug?) On Sun, 4 Nov 2001, Jeff Lu wrote: >Hi, >I'm getting parser error at or near AS >when try to copy a table using CREATE TABLE AS >Here what I have in the sql statement >CREATE TABLE employee_backup (id text UNIQUE, lastname text, firstname text, >phone text) AS SELECT * FROM employee >Can some body tell me what is wrong with the sql statement? I don't believe you can specify types or constraints. Also, if you specify the name of each column in parens, PostgreSQL seems to get confused if you do a SELECT * following AS, rather than specify each table name as well (as of 7.1.x, I get ERROR: CREATE TABLE/AS SELECT has mismatched column count - is this a known bug?) I believe this should work, though you lose the UNIQUE constraint: CREATE TABLE employee_backup AS SELECT * FROM employee; Regards, Jw. -- jlx@commandprompt.com by way of pgsql-general@commandprompt.com
Yes, it will be fixed in 7.2, which is the next release. --------------------------------------------------------------------------- > Thanks, > will this be fixed on the next release? > > -----Original Message----- > From: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Tom Lane > Sent: Sunday, November 04, 2001 9:02 PM > To: Command Prompt, Inc.; Jeff Lu; Postgresql General > Subject: Re: [GENERAL] Got error on CREATE TABLE AS (+Bug?) > > > Tom Lane <tgl@sss.pgh.pa.us> writes: > > "Command Prompt, Inc." <pgsql-general@commandprompt.com> writes: > >> lx=# CREATE TABLE abc (a char, b char, c char); > >> CREATE > >> lx=# CREATE TABLE xyz (x, y, z) AS SELECT * FROM abc; > >> ERROR: CREATE TABLE/AS SELECT has mismatched column count > >> lx=# CREATE TABLE xyz (x, y, z) AS SELECT a, b, c FROM abc; > >> SELECT > > > Looks like a bug to me too. Will look into it. > > Fix committed for 7.2. > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > -- 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