當應用程式呼叫 SQLFetch、 SQLFetchScroll或 SQLGetData時，驅動程式會從數據源擷取數據。 If necessary, it converts the data from the data type in which the driver retrieved it to the data type specified by the TargetType argument in SQLBindCol or SQLGetData. Finally, it stores the data in the location pointed to by the TargetValuePtr argument in SQLBindCol or SQLGetData (and the SQL_DESC_DATA_PTR field of the ARD).
下表顯示從 ODBC SQL 資料類型轉換成 ODBC C 資料類型的支持轉換。 A filled circle indicates the default conversion for a SQL data type (the C data type to which the data will be converted when the value of TargetType is SQL_C_DEFAULT). 空心圓表示支持的轉換。
For an ODBC 3.x application working with an ODBC 2.x driver, conversion from driver-specific data types might not be supported.
已轉換數據的格式不會受到 Windows 國家/地區設定的影響。
下列各節中的數據表說明驅動程式或數據源如何轉換從數據源擷取的數據;驅動程式必須支援從其支援的 ODBC SQL 資料類型轉換成所有 ODBC C 資料類型。 For a given ODBC SQL data type, the first column of the table lists the legal input values of the TargetType argument in SQLBindCol and SQLGetData. The second column lists the outcomes of a test, often using the BufferLength argument specified in SQLBindCol or SQLGetData, which the driver performs to determine whether it can convert the data. For each outcome, the third and fourth columns list the values placed in the buffers specified by the TargetValuePtr and StrLen_or_IndPtr arguments specified in SQLBindCol or SQLGetData after the driver has attempted to convert the data. (The StrLen_or_IndPtr argument corresponds to the SQL_DESC_OCTET_LENGTH_PTR field of the ARD.) The last column lists the SQLSTATE returned for each outcome by SQLFetch, SQLFetchScroll, or SQLGetData.
If the TargetType argument in SQLBindCol or SQLGetData contains an identifier for an ODBC C data type not shown in the table for a given ODBC SQL data type, SQLFetch, SQLFetchScroll, or SQLGetData returns SQLSTATE 07006 (Restricted data type attribute violation). If the TargetType argument contains an identifier that specifies a conversion from a driver-specific SQL data type to an ODBC C data type and this conversion isn't supported by the driver, SQLFetch, SQLFetchScroll, or SQLGetData returns SQLSTATE HYC00 (Optional feature not implemented).
Although it's not shown in the tables, the driver returns SQL_NULL_DATA in the buffer specified by the StrLen_or_IndPtr argument when the SQL data value is NULL. For an explanation of the use of StrLen_or_IndPtr when multiple calls are made to retrieve data, see the SQLGetData Function function description. When SQL data is converted to character C data, the character count returned in StrLen_or_IndPtr doesn't include the null-termination byte. If TargetValuePtr is a null pointer, SQLGetData returns SQLSTATE HY009 (Invalid use of null pointer); in SQLBindCol, this unbinds the column.
資料表中會使用下列詞彙和慣例：
數據位元組長度 是 可在 TargetValuePtr 中傳回的 C 數據位元組數，不論數據在傳回應用程式之前是否遭到截斷。 對於字串數據，這不包含 null 終止字元的空間。
位元位元組長度 是以字元格式顯示數據所需的位元組總數。 This is as defined for each C data type in the section Display Size, except that character byte length is in bytes while the display size is in characters.
Words in italics represent function arguments or elements of the SQL grammar. 如需文法元素的語法，請參閱 附錄 C：SQL 文法。
本節包含下列文章。