SQLFetch Function

SQLFetch Function

SQLFetch Function

Conformance: Version Introduced: ODBC 1.0 Standards Compliance: ISO 92

Summary: SQLFetch fetches the next rowset of data from the result set and returns data for all bound columns.

SQLRETURN SQLFetch(
     SQLHSTMT     StatementHandle);

Arguments

StatementHandle: [Input] Statement handle.

Returns

SQL_SUCCESS, SQL_SUCCESS_WITH_INFO, SQL_NO_DATA, SQL_STILL_EXECUTING, SQL_ERROR, or SQL_INVALID_HANDLE.

Diagnostics

When SQLFetch returns either SQL_ERROR or SQL_SUCCESS_WITH_INFO, an associated SQLSTATE value can be obtained by calling SQLGetDiagRec Function with a HandleType of SQL_HANDLE_STMT and a Handle of StatementHandle. The following table lists the SQLSTATE values typically returned by SQLFetch and explains each one in the context of this function; the notation "(DM)" precedes the descriptions of SQLSTATEs returned by the Driver Manager. The return code associated with each SQLSTATE value is SQL_ERROR, unless noted otherwise. If an error occurs on a single column, SQLGetDiagField can be called with a DiagIdentifier of SQL_DIAG_COLUMN_NUMBER to determine the column the error occurred on; and SQLGetDiagField can be called with a DiagIdentifier of SQL_DIAG_ROW_NUMBER to determine the row that contains that column.

For all those SQLSTATEs that can return SQL_SUCCESS_WITH_INFO or SQL_ERROR (except 01xxx SQLSTATEs), SQL_SUCCESS_WITH_INFO is returned if an error occurs on one or more, but not all, rows of a multirow operation, and SQL_ERROR is returned if an error occurs on a single-row operation.

SQLSTATE	Error	Description
01000	General warning	Driver-specific informational message. (Function returns SQL_SUCCESS_WITH_INFO.)
01004	String data, right truncated	String or binary data returned for a column resulted in the truncation of nonblank character or non-NULL binary data. If it was a string value, it was right-truncated.
01S01	Error in row	An error occurred while fetching one or more rows. (If this SQLSTATE is returned when an ODBC 3.x application is working with an ODBC 2.x driver, it can be ignored.)
01S07	Fractional truncation	The data returned for a column was truncated. For numeric data types, the fractional part of the number was truncated. For time, timestamp, and interval data types that contain a time component, the fractional part of the time was truncated. (Function returns SQL_SUCCESS_WITH_INFO.)
07006	Restricted data type attribute violation	The data value of a column in the result set could not be converted to the data type specified by TargetType in SQLBindCol. Column 0 was bound with a data type of SQL_C_BOOKMARK, and the SQL_ATTR_USE_BOOKMARKS statement attribute was set to SQL_UB_VARIABLE. Column 0 was bound with a data type of SQL_C_VARBOOKMARK, and the SQL_ATTR_USE_BOOKMARKS statement attribute was not set to SQL_UB_VARIABLE.
07009	Invalid descriptor index	The driver was an ODBC 2.x driver that does not support SQLExtendedFetch, and a column number specified in the binding for a column was 0. Column 0 was bound, and the SQL_ATTR_USE_BOOKMARKS statement attribute was set to SQL_UB_OFF.
08S01	Communication link failure	The communication link between the driver and the data source to which the driver was connected failed before the function completed processing.
22001	String data, right truncated	A variable-length bookmark returned for a column was truncated.
22002	Indicator variable required but not supplied	NULL data was fetched into a column whose StrLen_or_IndPtr set by SQLBindCol (or SQL_DESC_INDICATOR_PTR set by SQLSetDescField or SQLSetDescRec) was a null pointer.
22003	Numeric value out of range	Returning the numeric value as numeric or string for one or more bound columns would have caused the whole (as opposed to fractional) part of the number to be truncated. For more information, see Converting Data from SQL to C Data Types in Appendix D: Data Types.
22007	Invalid datetime format	A character column in the result set was bound to a date, time, or timestamp C structure, and a value in the column was, respectively, an invalid date, time, or timestamp.
22012	Division by zero	A value from an arithmetic expression was returned, which resulted in division by zero.
22015	Interval field overflow	Assigning from an exact numeric or interval SQL type to an interval C type caused a loss of significant digits in the leading field. When fetching data to an interval C type, there was no representation of the value of the SQL type in the interval C type.
22018	Invalid character value for cast specification	A character column in the result set was bound to a character C buffer, and the column contained a character for which there was no representation in the character set of the buffer. The C type was an exact or approximate numeric, a datetime, or an interval data type; the SQL type of the column was a character data type; and the value in the column was not a valid literal of the bound C type.
24000	Invalid cursor state	The StatementHandle was in an executed state but no result set was associated with the StatementHandle.
40001	Serialization failure	The transaction in which the fetch was executed was terminated to prevent deadlock.
40003	Statement completion unknown	The associated connection failed during the execution of this function, and the state of the transaction cannot be determined.
HY000	General error	An error occurred for which there was no specific SQLSTATE and for which no implementation-specific SQLSTATE was defined. The error message returned by SQLGetDiagRec in the *MessageText buffer describes the error and its cause.
HY001	Memory allocation error	The driver was unable to allocate memory that is required to support execution or completion of the function.
HY008	Operation canceled	Asynchronous processing was enabled for the StatementHandle. The function was called, and before it completed execution, SQLCancel was called on the StatementHandle. Then the function was called again on the StatementHandle. The function was called, and before it completed execution, SQLCancel was called on the StatementHandle from a different thread in a multithread application.
HY010	Function sequence error	(DM) The specified StatementHandle was not in an executed state. The function was called without first calling SQLExecDirect, SQLExecute or a catalog function. (DM) An asynchronously executing function (not this one) was called for the StatementHandle and was still executing when this function was called. (DM) SQLExecute, SQLExecDirect, SQLBulkOperations, or SQLSetPos was called for the StatementHandle and returned SQL_NEED_DATA. This function was called before data was sent for all data-at-execution parameters or columns. (DM) SQLFetch was called for the StatementHandle after SQLExtendedFetch was called and before SQLFreeStmt with the SQL_CLOSE option was called.
HY013	Memory management error	The function call could not be processed because the underlying memory objects could not be accessed, possibly because of low memory conditions.
HY090	Invalid string or buffer length	The SQL_ATTR_USE_BOOKMARK statement attribute was set to SQL_UB_VARIABLE, and column 0 was bound to a buffer whose length was not equal to the maximum length for the bookmark for this result set. (This length is available in the SQL_DESC_OCTET_LENGTH field of the IRD and can be obtained by calling SQLDescribeCol, SQLColAttribute, or SQLGetDescField.)
HY107	Row value out of range	The value specified with the SQL_ATTR_CURSOR_TYPE statement attribute was SQL_CURSOR_KEYSET_DRIVEN, but the value specified with the SQL_ATTR_KEYSET_SIZE statement attribute was greater than 0 and less than the value specified with the SQL_ATTR_ROW_ARRAY_SIZE statement attribute.
HYC00	Optional feature not implemented	The driver or data source does not support the conversion specified by the combination of the TargetType in SQLBindCol and the SQL data type of the corresponding column.
HYT01	Connection timeout expired	The connection timeout period expired before the data source responded to the request. The connection timeout period is set through SQLSetConnectAttr, SQL_ATTR_CONNECTION_TIMEOUT.
IM001	Driver does not support this function	(DM) The driver associated with the StatementHandle does not support the function.

Comments

SQLFetch returns the next rowset in the result set. It can be called only while a result set exists: that is, after a call that creates a result set and before the cursor over that result set is closed. If any columns are bound, it returns the data in those columns. If the application has specified a pointer to a row status array or a buffer in which to return the number of rows fetched, SQLFetch also returns this information. Calls to SQLFetch can be mixed with calls to SQLFetchScroll but cannot be mixed with calls to SQLExtendedFetch. For more information, see Fetching a Row of Data.

If an ODBC 3.x application works with an ODBC 2.x driver, the Driver Manager maps SQLFetch calls to SQLExtendedFetch for an ODBC 2.x driver that supports SQLExtendedFetch. If the ODBC 2.x driver does not support SQLExtendedFetch, the Driver Manager maps SQLFetch calls to SQLFetch in the ODBC 2.x driver, which can fetch only a single row.

For more information, see Block Cursors, Scrollable Cursors, and Backward Compatibility in Appendix G: Driver Guidelines for Backward Compatibility.

Positioning the Cursor

When the result set is created, the cursor is positioned before the start of the result set. SQLFetch fetches the next rowset. It is equivalent to calling SQLFetchScroll with FetchOrientation set to SQL_FETCH_NEXT. For more information about cursors, see Cursors and Block Cursors.

The SQL_ATTR_ROW_ARRAY_SIZE statement attribute specifies the number of rows in the rowset. If the rowset being fetched by SQLFetch overlaps the end of the result set, SQLFetch returns a partial rowset. That is, if S + R – 1 is greater than L, where S is the starting row of the rowset being fetched, R is the rowset size, and L is the last row in the result set, then only the first L – S + 1 rows of the rowset are valid. The remaining rows are empty and have a status of SQL_ROW_NOROW.

After SQLFetch returns, the current row is the first row of the rowset.

The rules listed in the following table describe cursor positioning after a call to SQLFetch, based on the conditions listed in the second table in this section.

Condition	First row of new rowset
Before start	1
CurrRowsetStart <= LastResultRow – RowsetSize[1]	CurrRowsetStart + RowsetSize[2]
CurrRowsetStart > LastResultRow – RowsetSize[1]	After end
After end	After end

[1] If the rowset size is changed between fetches, this is the rowset size that was used with the previous fetch.

[2] If the rowset size is changed between fetches, this is the rowset size that was used with the new fetch.

Notation	Meaning
Before start	The block cursor is positioned before the start of the result set. If the first row of the new rowset is before the start of the result set, SQLFetch returns SQL_NO_DATA.
After end	The block cursor is positioned after the end of the result set. If the first row of the new rowset is after the end of the result set, SQLFetch returns SQL_NO_DATA.
CurrRowsetStart	The number of the first row in the current rowset.
LastResultRow	The number of the last row in the result set.
RowsetSize	The rowset size.

For example, suppose a result set has 100 rows and the rowset size is 5. The following table shows the rowset and return code returned by SQLFetch for different starting positions.

Current rowset	Return code	New rowset	# of rows fetched
Before start	SQL_SUCCESS	1 to 5	5
1 to 5	SQL_SUCCESS	6 to 10	5
52 to 56	SQL_SUCCESS	57 to 61	5
91 to 95	SQL_SUCCESS	96 to 100	5
93 to 97	SQL_SUCCESS	98 to 100. Rows 4 and 5 of the row status array are set to SQL_ROW_NOROW.	3
96 to 100	SQL_NO_DATA	None.	0
99 to 100	SQL_NO_DATA	None.	0
After end	SQL_NO_DATA	None.	0

Returning Data in Bound Columns

As SQLFetch returns each row, it puts the data for each bound column in the buffer bound to that column. If no columns are bound, SQLFetch returns no data but does move the block cursor forward. The data can still be retrieved by using SQLGetData. If the cursor is a multirow cursor (that is, the SQL_ATTR_ROW_ARRAY_SIZE is greater than 1), SQLGetData can be called only if SQL_GD_BLOCK is returned when SQLGetInfo is called with an InfoType of SQL_GETDATA_EXTENSIONS. (For more information, see SQLGetData.)

For each bound column in a row, SQLFetch does the following:

Sets the length/indicator buffer to SQL_NULL_DATA and proceeds to the next column if the data is NULL. If the data is NULL and no length/indicator buffer was bound, SQLFetch returns SQLSTATE 22002 (Indicator variable required but not supplied) for the row and proceeds to the next row. For information about how to determine the address of the length/indicator buffer, see "Buffer Addresses" in SQLBindCol.

If the data for the column is not NULL, SQLFetch proceeds to step 2.

If the SQL_ATTR_MAX_LENGTH statement attribute is set to a nonzero value and the column contains character or binary data, the data is truncated to SQL_ATTR_MAX_LENGTH bytes.

Note
The SQL_ATTR_MAX_LENGTH statement attribute is intended to reduce network traffic. It is generally implemented by the data source, which truncates the data before returning it over the network. Drivers and data sources are not required to support it. Therefore, to guarantee that data is truncated to a particular size, an application should allocate a buffer of that size and specify the size in the cbValueMax argument in SQLBindCol.

Note

The SQL_ATTR_MAX_LENGTH statement attribute is intended to reduce network traffic. It is generally implemented by the data source, which truncates the data before returning it over the network. Drivers and data sources are not required to support it. Therefore, to guarantee that data is truncated to a particular size, an application should allocate a buffer of that size and specify the size in the cbValueMax argument in SQLBindCol.

Converts the data to the type specified by TargetType in SQLBindCol.
If the data was converted to a variable-length data type, such as character or binary, SQLFetch checks whether the length of the data exceeds the length of the data buffer. If the length of character data (including the null-termination character) exceeds the length of the data buffer, SQLFetch truncates the data to the length of the data buffer less the length of a null-termination character. It then null-terminates the data. If the length of binary data exceeds the length of the data buffer, SQLFetch truncates it to the length of the data buffer. The length of the data buffer is specified with BufferLength in SQLBindCol.

SQLFetch never truncates data converted to fixed-length data types; it always assumes that the length of the data buffer is the size of the data type.
Puts the converted (and possibly truncated) data in the data buffer. For information about how to determine the address of the data buffer, see "Buffer Addresses" in SQLBindCol.
Puts the length of the data in the length/indicator buffer. If the indicator pointer and the length pointer were both set to the same buffer (as a call to SQLBindCol does), the length is written in the buffer for valid data and SQL_NULL_DATA is written in the buffer for NULL data. If no length/indicator buffer was bound, SQLFetch does not return the length.
- For character or binary data, this is the length of the data after conversion and before truncation because of the data buffer being too small. If the driver cannot determine the length of the data after conversion, as is sometimes the case with long data, it sets the length to SQL_NO_TOTAL. If data was truncated because of the SQL_ATTR_MAX_LENGTH statement attribute, the value of this attribute is put in the length/indicator buffer instead of the actual length . This is because this attribute is designed to truncate data on the server before conversion, so that the driver has no way of figuring out what the actual length is.
- For all other data types, this is the length of the data after conversion; that is, it is the size of the type to which the data was converted.
For information about how to determine the address of the length/indicator buffer, see "Buffer Addresses" in SQLBindCol.
If the data is truncated during conversion without a loss of significant digits (for example, the real number 1.234 is truncated to the integer 1 when converted), SQLFetch returns SQLSTATE 01S07 (Fractional truncation) and SQL_SUCCESS_WITH_INFO. If the data is truncated because the length of the data buffer is too small (for example, the string "abcdef" is put in a 4-byte buffer), SQLFetch returns SQLSTATE 01004 (Data truncated) and SQL_SUCCESS_WITH_INFO. If data is truncated because of the SQL_ATTR_MAX_LENGTH statement attribute, SQLFetch returns SQL_SUCCESS and does not return SQLSTATE 01S07 (Fractional truncation) or SQLSTATE 01004 (Data truncated). If data is truncated during conversion with a loss of significant digits (for example, if an SQL_INTEGER value greater than 100,000 were converted to an SQL_C_TINYINT), SQLFetch returns SQLSTATE 22003 (Numeric value out of range) and SQL_ERROR (if the rowset size is 1) or SQL_SUCCESS_WITH_INFO (if the rowset size is greater than 1).

The contents of the bound data buffer and the length/indicator buffer are undefined if SQLFetch or SQLFetchScroll does not return SQL_SUCCESS or SQL_SUCCESS_WITH_INFO.

Row Status Array

The row status array is used to return the status of each row in the rowset. The address of this array is specified with the SQL_ATTR_ROW_STATUS_PTR statement attribute. The array is allocated by the application and must have as many elements as are specified by the SQL_ATTR_ROW_ARRAY_SIZE statement attribute. Its values are set by SQLFetch, SQLFetchScroll, and SQLBulkOperations or SQLSetPos (except when they have been called after the cursor has been positioned by SQLExtendedFetch). If the value of the SQL_ATTR_ROW_STATUS_PTR statement attribute is a null pointer, these functions do not return the row status.

The contents of the row status array buffer are undefined if SQLFetch or SQLFetchScroll does not return SQL_SUCCESS or SQL_SUCCESS_WITH_INFO.

The following values are returned in the row status array.

Row status array value	Description
SQL_ROW_SUCCESS	The row was successfully fetched and has not changed since it was last fetched from this result set.
SQL_ROW_SUCCESS_WITH_INFO	The row was successfully fetched and has not changed since it was last fetched from this result set. However, a warning was returned about the row.
SQL_ROW_ERROR	An error occurred while fetching the row.
SQL_ROW_UPDATED[1],[2], and [3]	The row was successfully fetched and has changed since it was last fetched from this result set. If the row is fetched again from this result set or is refreshed by SQLSetPos, the status is changed to the row's new status.
SQL_ROW_DELETED[3]	The row has been deleted since it was last fetched from this result set.
SQL_ROW_ADDED[4]	The row was inserted by SQLBulkOperations. If the row is fetched again from this result set or is refreshed by SQLSetPos, its status is SQL_ROW_SUCCESS.
SQL_ROW_NOROW	The rowset overlapped the end of the result set, and no row was returned that corresponded to this element of the row status array.

[1] For keyset, mixed, and dynamic cursors, if a key value is updated, the row of data is considered to have been deleted and a new row added.

[2] Some drivers cannot detect updates to data and therefore cannot return this value. To determine whether a driver can detect updates to refetched rows, an application calls SQLGetInfo with the SQL_ROW_UPDATES option.

[3] SQLFetch can return this value only when it is intermixed with calls to SQLFetchScroll. This is because SQLFetch moves forward through the result set and when it is used exclusively, does not refetch any rows. Because no rows are refetched, SQLFetch does not detect changes that were made to previously fetched rows. However, if SQLFetchScroll positions the cursor before any previously fetched rows and SQLFetch is used to fetch those rows, SQLFetch can detect any changes to those rows.

[4] Returned by SQLBulkOperations only. Not set by SQLFetch or SQLFetchScroll.

Rows Fetched Buffer

The rows fetched buffer is used to return the number of rows fetched, including those rows for which no data was returned because an error occurred while they were being fetched. In other words, it is the number of rows for which the value in the row status array is not SQL_ROW_NOROW. The address of this buffer is specified with the SQL_ATTR_ROWS_FETCHED_PTR statement attribute. The buffer is allocated by the application. It is set by SQLFetch and SQLFetchScroll. If the value of the SQL_ATTR_ROWS_FETCHED_PTR statement attribute is a null pointer, these functions do not return the number of rows fetched. To determine the number of the current row in the result set, an application can call SQLGetStmtAttr with the SQL_ATTR_ROW_NUMBER attribute.

The contents of the rows fetched buffer are undefined if SQLFetch or SQLFetchScroll does not return SQL_SUCCESS or SQL_SUCCESS_WITH_INFO, except when SQL_NO_DATA is returned, in which case the value in the rows fetched buffer is set to 0.

Error Handling

Errors and warnings can apply to individual rows or to the whole function. For more information about diagnostic records, see Diagnostics and SQLGetDiagField.

Errors and Warnings on the Entire Function

If an error applies to the entire function, such as SQLSTATE HYT00 (Timeout expired) or SQLSTATE 24000 (Invalid cursor state), SQLFetch returns SQL_ERROR and the applicable SQLSTATE. The contents of the rowset buffers are undefined and the cursor position is unchanged.

If a warning applies to the entire function, SQLFetch returns SQL_SUCCESS_WITH_INFO and the applicable SQLSTATE. The status records for warnings that apply to the entire function are returned before the status records that apply to individual rows.

Errors and Warnings in Individual Rows

If an error (such as SQLSTATE 22012 (Division by zero)) or a warning (such as SQLSTATE 01004 (Data truncated)) applies to a single row, SQLFetch does the following:

Sets the corresponding element of the row status array to SQL_ROW_ERROR for errors or SQL_ROW_SUCCESS_WITH_INFO for warnings.
Adds zero or more status records that contain SQLSTATEs for the error or warning.
Sets the row and column number fields in the status records. If SQLFetch cannot determine a row or column number, it sets that number to SQL_ROW_NUMBER_UNKNOWN or SQL_COLUMN_NUMBER_UNKNOWN, respectively. If the status record does not apply to a particular column, SQLFetch sets the column number to SQL_NO_COLUMN_NUMBER.

SQLFetch continues fetching rows until it has fetched all the rows in the rowset. It returns SQL_SUCCESS_WITH_INFO unless an error occurs in every row of the rowset (not including rows with status SQL_ROW_NOROW), in which case it returns SQL_ERROR. In particular, if the rowset size is 1 and an error occurs in that row, SQLFetch returns SQL_ERROR.

SQLFetch returns the status records in row number order. That is, it returns all status records for unknown rows (if any); next it returns all status records for the first row (if any), and then it returns all status records for the second row (if any), and so on. The status records for each row are ordered according to the normal rules for ordering status records; for more information, see "Sequence of Status Records" in SQLGetDiagField.

Descriptors and SQLFetch

The following sections describe how SQLFetch interacts with descriptors.

Argument Mappings

The driver does not set any descriptor fields based on the arguments of SQLFetch.

Other Descriptor Fields

The following descriptor fields are used by SQLFetch.

Descriptor field	Desc.	Field in	Set through
SQL_DESC_ARRAY_SIZE	ARD	header	SQL_ATTR_ROW_ARRAY_SIZE statement attribute
SQL_DESC_ARRAY_STATUS_PTR	IRD	header	SQL_ATTR_ROW_STATUS_PTR statement attribute
SQL_DESC_BIND_OFFSET_PTR	ARD	header	SQL_ATTR_ROW_BIND_OFFSET_PTR statement attribute
SQL_DESC_BIND_TYPE	ARD	header	SQL_ATTR_ROW_BIND_TYPE statement attribute
SQL_DESC_COUNT	ARD	header	ColumnNumber argument of SQLBindCol
SQL_DESC_DATA_PTR	ARD	records	TargetValuePtr argument of SQLBindCol
SQL_DESC_INDICATOR_PTR	ARD	records	StrLen_or_IndPtr argument in SQLBindCol
SQL_DESC_OCTET_LENGTH	ARD	records	BufferLength argument in SQLBindCol
SQL_DESC_OCTET_LENGTH_PTR	ARD	records	StrLen_or_IndPtr argument in SQLBindCol
SQL_DESC_ROWS_PROCESSED_PTR	IRD	header	SQL_ATTR_ROWS_FETCHED_PTR statement attribute
SQL_DESC_TYPE	ARD	records	TargetType argument in SQLBindCol

All descriptor fields can also be set through SQLSetDescField.

Separate Length and Indicator Buffers

Applications can bind a single buffer or two separate buffers that can be used to hold length and indicator values. When an application calls SQLBindCol, the driver sets the SQL_DESC_OCTET_LENGTH_PTR and SQL_DESC_INDICATOR_PTR fields of the ARD to the same address, which is passed in the StrLen_or_IndPtr argument. When an application calls SQLSetDescField or SQLSetDescRec, it can set these two fields to different addresses.

SQLFetch determines whether the application has specified separate length and indicator buffers. In this case, when the data is not NULL, SQLFetch sets the indicator buffer to 0 and returns the length in the length buffer. When the data is NULL, SQLFetch sets the indicator buffer to SQL_NULL_DATA and does not modify the length buffer.

Code Example

See SQLBindCol, SQLColumns, SQLGetData, and SQLProcedures.

Related Functions

For information about	See
Binding a buffer to a column in a result set	SQLBindCol Function
Canceling statement processing	SQLCancel Function
Returning information about a column in a result set	SQLDescribeCol Function
Executing an SQL statement	SQLExecDirect Function
Executing a prepared SQL statement	SQLExecute Function
Fetching a block of data or scrolling through a result set	SQLFetchScroll Function
Closing the cursor on the statement	SQLFreeStmt Function
Fetching part or all of a column of data	SQLGetData Function
Returning the number of result set columns	SQLNumResultCols Function
Preparing a statement for execution	SQLPrepare Function