DataBlade API Programmer's Manual

DataBlade API Programmer's Manual
Chapter 7: Processing Results

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Using Supporting Functions

In addition to mi_get_result(), other functions report information about the results of the current statement.

The mi_result_command_name() function reports the kind of statement (such as SELECT, INSERT, UPDATE, CREATE, or DROP) as a null-terminated character string. This function might be useful in an interactive application in which the statement sent is not determined until runtime. This function should be used only when mi_get_result() reports that a DML statement completed.

The mi_result_row_count() function returns the number of rows affected by a statement. It is applicable only when mi_get_result() reports that a DML statement completed.

Important: If you want a count of the number of rows that satisfy a given query but you do not want the data in the rows, you can run a query that uses the count aggregate more efficiently than you can run a query that returns the actual rows. For example, the following query counts the number of rows in mytable:

select count(*) from mytable;

Example: get_results()

The following user-defined function, get_results(), demonstrates an mi_get_result() loop. It also demonstrates the mi_result_command_name() function to get the name of the statement and the mi_result_row_count() function to get the number of rows affected by the statement.

When a query returns rows of data, the get_results() example routine calls another user-defined function, get_data(), to iterate over the rows. For information on how to process the returned rows, see "Fetching Data".

Following the mi_exec() function for a typical SELECT query, mi_get_result() first returns MI_ROWS to indicate that row data is available. The example get_data() function then iterates over all the rows and returns control to the top of the loop. The next call to mi_get_result() returns MI_DML because a data manipulation statement was completed (the iteration in get_data() completed it). A final call to mi_get_result() returns MI_NO_MORE_RESULTS, and the loop terminates.

/*
*  Gets results of current statement,
*  displays the kind of statement and number of rows
*  affected, and returns the number of rows affected
*/
#include "mi.h"
 
int
get_results( MI_CONNECTION * conn )
   {
   mi_integer   count;
   mi_integer   result;
   char         cmd [25];
 
   while ( ( result = mi_get_result( conn ) ) != MI_NO_MORE_RESULTS )
      {
 
      switch( result )
         {
         case MI_ERROR:
            mi_db_error_raise( conn, MI_MESSAGE, "Could not get results\n" );
            return( -1 );
            break;
 
         case MI_DDL:
            break;
 
         case MI_DML:
            /* what kind of statement was it? */
            cmd = mi_result_command_name( conn );
 
            /* get # rows affected by statement */
            count = mi_result_row_count( conn );
            if ( MI_ERROR == count )
               {
               mi_db_error_raise( conn, MI_MESSAGE, "Cannot get row count\n" );
               return( -1 );
               }
            else
               {
               mi_db_error_raise( conn, MI_MESSAGE, "Rows Returned\n" );
               }
            break;
case MI_ROWS:
            get_data( conn );
            break;
 
         default:
            mi_db_error_raise( conn, MI_MESSAGE, "Unknown results\n" );
            return( -1 );
         }
      }
 
   return ( count );
   }

DataBlade API Programmer's ManualChapter 7: Processing Results Home Contents Index Master Index New Book

Using Supporting Functions

Example: get_results()

DataBlade API Programmer's Manual
Chapter 7: Processing Results

Home Contents Index Master Index New Book