The EXTFNAPIV4_DESCRIBE_COL_VALUES_SUBSET_OF_INPUT attribute sets a subset of the values specified in an input column. Used in a describe_column_set scenario.
a_v4_extfn_col_subset_of_input
Column values are a subset of the values specified in an input column.
Setting this describe attribute informs the query optimizer that the indicated column values are a subset of those values specified in an input column. For example, consider a filter TPF that consumes a table and filters out rows based on a function. In such a case, the return table is a subset of the input table. Setting EXTFNAPIV4_DESCRIBE_COL_VALUES_SUBSET_OF_INPUT for the filter TPF optimizes the query.
On success, returns the sizeof(a_v4_extfn_col_subset_of_input).
On failure, returns one of the generic describe_column errors, or:
Valid in:
a_v4_extfn_col_subset_of_input colMap; colMap.source_table_parameter_arg_num = 4; colMap.source_column_number = i; desc_rc = ctx->describe_column_set( ctx, 0, i, EXTFNAPIV4_DESCRIBE_COL_VALUES_SUBSET_OF_INPUT, &colMap, sizeof(a_v4_extfn_col_subset_of_input) );