Process complex qualifications

In the following figure, the am_getnext purpose function attempts to disqualify source records. It creates rows for fully qualified source records and for those rows that it cannot disqualify.

Figure 1. Sample am_getnext purpose function

mi_integer sample_getnext(sd,retrow,retrowid)
   MI_AM_SCAN_DESC *sd;
   MI_ROW             **retrow
   mi_integer         retrowid; 
{
   my_data_t    *my_data;
   MI_ROW_DESC *rd;
   MI_AM_TABLE_DESC *td;
   MI_AM_QUAL_DESC  *qd;
   td = mi_scan_table(sd); /* Get table descriptor. */
   rd = mi_tab_rowdesc(td); /* Get column data types. */
   my_data = (my_data_t *)mi_tab_userdata(td); /* Get pointer to user data.*/
   MI_DATUM    qdvalue;
   /* Evaluate records until one qualifies for return to caller.. */
   for (;;)
   {
      /* Test for and exit if end of data. (more_rows() routine not shown.)*/ 
      if (more_rows(my_data) !=MI_OK) 
         return MI_NO_MORE_RESULTS;
      /* User data contains more rows, so evaluate the next one */
      get_results(qd, my_data);
      qdvalue = mi_qual_value(qd)
      if (qdvalue == MI_VALUE_TRUE)
      {
         /*Create MI_ROW and return it to the database server. */
         *retrow = mi_row_create(...);
         return MI_ROWS;
      }
      else if (qdvalue == MI_VALUE_NOT_EVALUATED)
       {
         /*Create MI_ROW and return it to the database server. */
         *retrow = mi_row_create(...);
         if (mi_eval_am_qual(retrow, qd) == MI_VALUE_TRUE)
            return MI_ROWS;
      }
      /* Either get_result() or mi_eval_am_qual() returned MI_VALUE_FALSE. */
      mi_init_am_qual(qd); /* Reset qualification descriptor */
      my_data->rowptr++;
   } /*End loop.*/
}/* End getnext.*/

In the next figure, the get_result() function loops recursively through the qualification descriptor, looking for simple qualifications that the access method knows how to evaluate. It sets results for the simple qualifications and leaves MI_VALUE_NOT_EVALUATED in the Boolean-operator portions of the qualification descriptor.

Tip: The examples in this topic do not illustrate the code that the access method uses to execute functions.

Figure 2. Setting results in the qualification descriptor

  

... get_result(qd, my_data)
   MI_AM_QUAL_DESC   *qd;
   user_data_t                     *my_data
{
   if (mi_qual_issimple(qd))  
   { 
      /* Execute simple, function. (Not shown.) */
      /* Test the result that the function returns. */
      if (result == MI_TRUE) 
      {
         /* Set result in qualification descriptor.*/
         mi_qual_setvalue(qd,MI_VALUE_TRUE);
         return; ;
      }
      else 
      {
         mi_qual_setvalue( qd,MI_VALUE_FALSE);
         return;;
      } 
   } /* END: if (mi_qual_issimple(qd)) */
   else
   {/*Complex qualification (has AND or OR)..Loop until all functions execute.*/
      for (i = 0; i < mi_qual_nquals(qd); i++) 
         get_result(mi_qual_qual(qd, i), my_data)
   } /* END: Complex qualification (has AND or OR)*/
   return;;