date:20140324

Re: [HACKERS] using arrays within structure in ECPG

2014-03-24 Thread Ashutosh Bapat

On Mon, Mar 24, 2014 at 3:40 PM, Boszormenyi Zoltan  wrote:

>  2014-03-24 07:22 keltezéssel, Ashutosh Bapat írta:
>
>  Hi,
>  I tried using integer array within a structure array in ECPG code. But
> it resulted in some garbage values being printed from the table. Here are
> the details,
>
>  The ECPG program is attached (array_test.pgc). It tries to read the
> contents of table emp, whose structure and contents are as follows
> postgres=# \d+ emp
>Table "public.emp"
>  Column  |   Type| Modifiers | Storage  | Stats target |
> Description
>
> -+---+---+--+--+-
>  empno   | numeric(4,0)  |   | main |  |
>  ename   | character varying |   | extended |  |
>  job | character varying |   | extended |  |
>  arr_col | integer[] |   | extended |  |
> Has OIDs: no
>
> postgres=# select * from emp;
>  empno | ename  |   job   |  arr_col
> ---++-+
>   7900 | JAMES  | CLERK   | {1,2,7900}
>   7902 | FORD   | ANALYST | {1,2,7902}
>   7934 | MILLER | CLERK   | {1,2,7934}
> (3 rows)
>
>  You will notice that the last element of the arr_col array is same as
> the empno of that row.
>
>  The ECPG program tries to read the rows using FETCH in a structure emp
> defined as
>  15 struct employee {
>  16 int empno;
>  17char ename[11];
>  18char job[15];
>  19int  arr_col[3];
>  20 };
>
>  and then print the read contents as
>  39 /* Print members of the structure. */
>  40 for ( i = 0 ;i < 3; i++){
>  41 printf("empno=%d, ename=%s, job=%s, arr_col[2]=%d\n",
> emp[i].empno, emp[i].ename, emp[i].job, emp[i].arr_col[2]);
>  42
>  43 }
>
>  But garbage values are printed
> [ashutosh@ubuntu repro]./array_test
>
> +++
> empno=7900, ename=JAMES, job=CLERK, arr_col[2]=1
> empno=2, ename=� , job=ANALYST, arr_col[2]=32767
> empno=7934, ename=MILLER, job=CLERK, arr_col[2]=1719202336
>
>  Here are steps I have used to compile the ECPG program
> [ashutosh@ubuntu repro]make array_test
> ecpg -c -I/work/pg_head/build/include array_test.pgc
> cc -I/work/pg_head/build/include -g   -c -o array_test.o array_test.c
> cc -g  array_test.o  -L/work/pg_head/build/lib -lecpg -lpq -o array_test
> rm array_test.o array_test.c
>
>  where /work/pg_head/build is the directory containing the postgresql
> build (essentially argument to the --prefix option to configure).
>
>  The programs compiles and links fine.
>
>  Without the arr_col member, the program works fine. So, it seems to be a
> problem with array within structure array.
>
>  In array_test.c I see that the ECPGdo statement corresponding to the
> FETCH command is as follows
>  87 /* Fetch multiple columns into one structure. */
>  88 { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "fetch 3 from
> cur1", ECPGt_EOIT,
>  89 ECPGt_int,&(emp->empno),(long)1,(long)14,sizeof( struct employee ),
>  90 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
>  91 ECPGt_char,&(emp->ename),(long)11,(long)14,sizeof( struct employee
> ),
>  92 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
>  93 ECPGt_char,&(emp->job),(long)15,(long)14,sizeof( struct employee ),
>  94 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
>  95 ECPGt_int,(emp->arr_col),(long)1,(long)3,sizeof(int),
>  96 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
>
>  For all the members of struct employee, except arr_col, the size of
> array is set to 14 and next member offset is set of sizeof (struct
> employee). But for arr_col they are set to 3 and sizeof(int) resp. So, for
> the next row onwards, the calculated offset of arr_col member would not
> coincide with the real arr_col member's address.
>
>  Am I missing something here?
>
>
> ECPG (I think intentionally) doesn't interpret or parse array fields.
> You need to pass a character array and parse the contents by yourself.
>
>
That doesn't seem to be the case with bare arrays (not included in anything
else). I added following lines to the program attached in my first mail,
and they worked perfectly fine.

 47 /* Test only arrays */
 48 EXEC SQL DECLARE cur2 CURSOR FOR select arr_col from emp;
 49
 50 EXEC SQL OPEN cur2;
 51
 52 EXEC SQL FETCH 1 FROM cur2 into :emp[0].arr_col;
 53
 54 printf("\n+++\n");
 55
 56 /* Print members of the array fetched. */
 57 for ( i = 0 ;i < 3; i++)
 58 {
 59 printf("arr_col[%d] = %d\n", i, emp[0].arr_col[i]);
 60 }
 61 EXEC SQL CLOSE cur2;

Anyway, if that's a restriction, shouldn't there be an error during
compilation?

> Best regards,
> Zoltán Böszörményi
>
>
>   --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>
>
>
>


-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporat

Re: [HACKERS] About adding an attribute to pg_attibute

2014-03-24 Thread Craig Ringer

On 03/25/2014 01:44 AM, Tanmay Deshpande wrote:
> We are trying add columnar support to postgreSQL and for that we need
> identify each column in each relation by an oid. So my doubt is how do
> we add an attribute/ a column to catalog pg_attribute ?

Is this some kind of class project?

I've seen at least three people post short, uninformative questions
about somewhat similar topics to this mailing list, all from gmail
addresses, in the last couple of days.

Rajashree Mandaogane
Swapnil Bhoite
Tanmay Deshpande

Ah, yes, it is something like that:

http://www.postgresql.org/message-id/capn0l0oxp9afnr7uhwzkytvzzyy8z-aqgfnpnabk-cgscge...@mail.gmail.com

To make it easier to understand your questions and their context, in
future please:

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on, so we know who you are. There are lots of people doing lots of
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Say so. If you found it helpful, you can always follow up with a
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Putting more effort into your questions will get you better answers.

--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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