The structure a_v4_extfn_column_data represents a single column's worth of data. This is used by the producer when generating result set data, or by the consumer when reading input table column data.
typedef struct a_v4_extfn_column_data {
a_sql_byte *is_null;
a_sql_byte null_mask;
a_sql_byte null_value;
void *data;
a_sql_uint32 *piece_len;
size_t max_piece_len;
void *blob_handle;
} a_v4_extfn_column_data;
| Data Member | Data Type | Description |
|---|---|---|
| is_null | a_sql_byte * | Points to a byte where the NULL information for the value is stored. |
| null_mask | a_sql_byte | One or more bits used to represent the NULL value |
| null_value | a_sql_byte | The value representing NULL |
| data | void * | Pointer to the data for the column. Depending on the type of fetch mechanism, either points to an address in the consumer, or an address where the data is stored in the UDF. |
| piece_len | a_sql_uint32 * | The actual length of data for variable-length data types |
| max_piece_len | size_t | The maximum data length allowed for this column. |
| blob_handle | void * | A non-NULL value means that the data for this column must be read using the blob API |
The a_v4_extfn_column_data structure represents the data values and related attributes for a specific data column. This structure is used by the producer when generating result set data. Data producers are also expected to create storage for data, piece_len, and the is_null flag.
The is_null, null_mask, and null_value data members indicate null in a column, and handle situations in which the null-bits are encoded into one byte for eight columns, or other cases in which a full byte is used for each column.
This example shows how to interpret the three fields used to represent NULL: is_null, null_mask, and null_value.
is_value_null() return( (*is_null & null_mask) == null_value ) set_value_null() *is_null = ( *is_null & ~null_mask) | null_value set_value_not_null() *is_null = *is_null & ~null_mask | (~null_value & null_mask)