Re: SQLNumResultCols before SQLExecute

Correct solution is to issue the prepare and read reply from server...
As should do... I'll check this out.

freddy77

2011/3/12 Dylan Kucera <[email protected]>:
> The following post is unrelated to the issue I just posted with respect to
> the "handle 0" problem with TDS 8.0 that I just posted.
>
> I was hoping to get some feedback on a work-around that I created for the
> limitation where FreeTDS cannot determine the answer for SQLNumResultCols
> after only calling SQLPrepare.  As designed, from what I understand,
> SQLExecute must be called first.
>
> I'm working with the Oracle Heterogenous Services database link capability
> so I have no ability to change the approach it takes, and in some
> scenarios it asks for SQLNumResultCols after only doing a SQLPrepare.
>
> From what I've observed, I believe I can count on the structure of the
> statement where this occurs to be
>
> SELECT "c1", "c2", ..., "cn" FROM "t1" WHERE ...
>
> So, assuming there is no reason to believe the database link has chosen
> invalid columns (which it won't because it's already confirmed the column
> list with sp_columns!  It just seems to have obsessive compulsive
> disorder!) then counting the commas before the FROM and adding one does
> the trick.
>
> I know it's not the most elegant thing in the world but after doing this I
> can use my Oracle Heterogeneous Services database links just fine.  For
> those who generally work on the FreeTDS code, would you consider putting
> something like this into the main code line for those of us wishing to use
> FreeTDS in this use case?  Would it really be worse than returning 0?
>
> Perhaps at the least this helps someone else out, though I'd be open to
> any cautionary tales if someone has already been down this path.
>
> in odbc.c, 2 changes:
>
> 1) Near line 1320:  redefine IRD_UPDATE as per another post I found where
> someone had a similar problem:
>
> #define IRD_UPDATE(desc, errs, exit) do { } while(0)
>
> #if 0
> #define IRD_UPDATE(desc, errs, exit) \
>        do { \
>                if (desc->type == DESC_IRD && ((TDS_STMT*)desc->parent)->need_reprepare && \
>                    odbc_update_ird((TDS_STMT*)desc->parent, errs) != SQL_SUCCESS) \
>                        exit; \
>        } while(0)
> #endif
>
> 2) Near line 4425: redefine SQLNumResultCols as follows:
>
> SQLRETURN ODBC_API
> SQLNumResultCols(SQLHSTMT hstmt, SQLSMALLINT FAR * pccol)
> {
> char *s;
> char *p;
> long c;
>
>        INIT_HSTMT;
>
>
>        tdsdump_log(TDS_DBG_FUNC, "SQLNumResultCols(%p, %p)\n",
>                        hstmt, pccol);
>
>        /*
>         * 3/15/2001 bsb - DBD::ODBC calls SQLNumResultCols on non-result
>         * generating queries such as 'drop table'
>         */
> #if 0
>        if (stmt->row_status == NOT_IN_ROW) {
>                odbc_errs_add(&stmt->errs, "24000", NULL);
>                ODBC_RETURN(stmt, SQL_ERROR);
>        }
> #endif
>        IRD_UPDATE(stmt->ird, &stmt->errs, ODBC_RETURN(stmt, SQL_ERROR));
>        *pccol = stmt->ird->header.sql_desc_count;
>
>
>        if (stmt->ird->header.sql_desc_count == 0) {
> tdsdump_log(TDS_DBG_FUNC, "SQLNumResultCols(%p, %p) - Desparate measures - parse from %s\n",
> hstmt, pccol, stmt->prepared_query);
>                s = malloc (strlen(stmt->prepared_query) + 64);
>                strcpy(s, stmt->prepared_query);
>                strupr(s);
>                p = strstr(s, " FROM ");
>                if (p != 0) {
>                        *p = '\0';
>                        c = 1;
>                        p = s;
>                        while ((p = strchr(p+1, ',')) != 0) {
>                                ++c;
>                        }
>                        *pccol = c;
>                }
>                free(s);
>        }
>
>
> tdsdump_log(TDS_DBG_FUNC, "SQLNumResultCols(%p, %p) = %d\n",
> hstmt, pccol, *pccol);
>
>
>        ODBC_RETURN_(stmt);
> }
>
>
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