mi_smallint * mi_scan_projs(MI_AM_SCAN_DESC *scanDesc)

scanDesc

points to the scan descriptor.

Use the return value from mi_scan_nprojs() to determine the number of times to execute mi_scan_projs(). Then use mi_scan_projs() to identify columns that the return row must contain.

A qualification identifies a column by a number that locates the column in the row descriptor. The number 0 indicates the first column in the row descriptor. In the following example, mi_scan_projs() points to the values 1, 5, and 4:

SELECT column1, column5, column4 FROM table 

The row descriptor describes the columns in the order that they appear in the CREATE TABLE statement. The following example shows how to determine the data type of each projected column:

MI_TYPE_DESC *typedesc; 
MI_AM_TABLE_DESC*td;
MI_ROW_DESC *rd;
MI_AM_SCAN_DESC*sd;
mi_integer  n;
mi_smallint c, *projcols;   /* column identifiers */
rd = mi_tab_rowdesc(td);    /* describes a table row*/
n = mi_scan_nprojs(sd); /*How many columns are projected?*/
projcols=mi_scan_projs(sd);/* identifies projected columns*/

for (int i = 0; i < n; i++)
{
   c = projcols[i];       /* Get offset to row descriptor.*/
   /* Get data type for projected column. For example 
   ** my_data->col_type[c] = mi_column_typedesc(rd, c) */
}

Each of the small integers in the array that this function returns identifies a column by the position of that column in the row descriptor.

See the descriptions of:

• Accessor functions mi_scan_nprojs(), mi_scan_table(), and mi_tab_rowdesc()
• The mi_column_* group of DataBlade API functions and the row descriptor (MI_ROW_DESC data structure) in the IBM Informix: DataBlade API Programmer's Guide