Conformance
Version Introduced:ODBC 3.0
Standards Compliance:ISO 92
Summary
SQLColAttribute returns descriptor information for a column in a result set. Descriptor information is returned as a character string, a 32-bit descriptor-dependent value, or an integer value.
Note For more information about what the Driver Manager maps this function to when an ODBC 3.x application is working with an ODBC 2.x driver, see “Mapping Replacement Functions for Backward Compatibility of Applications” in Chapter 17, “Programming Considerations.”
Syntax
SQLRETURN SQLColAttribute (
SQLHSTMTStatementHandle,
SQLUSMALLINTColumnNumber,
SQLUSMALLINTFieldIdentifier,
SQLPOINTERCharacterAttributePtr,
SQLSMALLINTBufferLength,
SQLSMALLINT *StringLengthPtr,
SQLPOINTERNumericAttributePtr);
Arguments
StatementHandle
[Input]
Statement handle.
ColumnNumber
[Input]
The number of the record in the IRD from which the field value is to be retrieved. This argument corresponds to the column number of result data, ordered sequentially in increasing column order, starting at 1. Columns can be described in any order.
Column 0 can be specified in this argument, but all values except SQL_DESC_TYPE and SQL_DESC_OCTET_LENGTH will return undefined values.
FieldIdentifier
[Input]
The field in row ColumnNumber of the IRD that is to be returned (see “Comments”).
CharacterAttributePtr
[Output]
Pointer to a buffer in which to return the value in the FieldIdentifier field of the ColumnNumber row of the IRD, if the field is a character string. Otherwise, the field is unused.
BufferLength
[Input]
If FieldIdentifier is an ODBC-defined field and CharacterAttributePtr points to a character string or binary buffer, this argument should be the length of *CharacterAttributePtr. If FieldIdentifier is an ODBC-defined field and *CharacterAttributePtr is an integer, this field is ignored. If the *CharacterAttributePtr is a Unicode string (when calling SQLColAttributeW), the BufferLength argument must be an even number. If FieldIdentifier is a driver-defined field, the application indicates the nature of the field to the Driver Manager by setting the BufferLength argument. BufferLength can have the following values:
StringLengthPtr
[Output]
Pointer to a buffer in which to return the total number of bytes (excluding the null-termination byte for character data) available to return in *CharacterAttributePtr.
For character data, if the number of bytes available to return is greater than or equal to BufferLength, the descriptor information in *CharacterAttributePtr is truncated to BufferLength minus the length of a null-termination character and is null-terminated by the driver.
For all other types of data, the value of BufferLength is ignored and the driver assumes the size of *CharacterAttributePtr is 32 bits.
NumericAttributePtr
[Output]
Pointer to an integer buffer in which to return the value in the FieldIdentifier field of the ColumnNumber row of the IRD, if the field is a numeric descriptor type, such as SQL_DESC_COLUMN_LENGTH. Otherwise, the field is unused.
Returns
SQL_SUCCESS, SQL_SUCCESS_WITH_INFO, SQL_STILL_EXECUTING, SQL_ERROR, or SQL_INVALID_HANDLE.
Diagnostics
When SQLColAttribute returns either SQL_ERROR or SQL_SUCCESS_WITH_INFO, an associated SQLSTATE value may be obtained by calling SQLGetDiagRec with a HandleType of SQL_HANDLE_STMT and a Handle of StatementHandle. The following table lists the SQLSTATE values commonly returned by SQLColAttribute 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.
| SQLSTATE | Error | Description |
| 01000 | General warning | Driver-specific informational message. (Function returns SQL_SUCCESS_WITH_INFO.) |
| 01004 | String data, right truncated | The buffer *CharacterAttributePtr was not large enough to return the entire string value, so the string value was truncated. The length of the untruncated string value is returned in *StringLengthPtr. (Function returns SQL_SUCCESS_WITH_INFO.) |
| 07005 | Prepared statement not a cursor-specification | The statement associated with the StatementHandle did not return a result set and FieldIdentifier was not SQL_DESC_COUNT. There were no columns to describe. |
| 07009 | Invalid descriptor index | (DM) The value specified for ColumnNumber was equal to 0, and the SQL_ATTR_USE_BOOKMARKS statement attribute was SQL_UB_OFF. The value specified for the argument ColumnNumber was greater than the number of columns in the result set. |
| 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 SQLGetDiagField from the diagnostic data structure describes the error and its cause. |
| HY001 | Memory allocation error | The driver was unable to allocate memory 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 function was called prior to calling SQLPrepare, SQLExecDirect, or a catalog function for the StatementHandle. (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. |
| 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 | (DM) *CharacterAttributePtr is a character string, and BufferLength was less than 0, but not equal to SQL_NTS. |
| HY091 | Invalid descriptor field identifier | The value specified for the argument FieldIdentifier was not one of the defined values, and was not an implementation-defined value. |
| HYC00 | Driver not capable | The value specified for the argument FieldIdentifier was not supported by the driver. |
| 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. |
SQLColAttribute can return any SQLSTATE that can be returned by SQLPrepare or SQLExecute when called after SQLPrepare and before SQLExecute, depending on when the data source evaluates the SQL statement associated with the StatementHandle.
For performance reasons, an application should not call SQLColAttribute before executing a statement.
Comments
For information about how applications use the information returned by SQLColAttribute, see “Result Set Metadata” in Chapter 10, “Retrieving Results (Basic).”
SQLColAttribute returns information either in *NumericAttributePtr or in *CharacterAttributePtr. Integer information is returned in *NumericAttributePtr as a 32-bit, signed value; all other formats of information are returned in *CharacterAttributePtr. When information is returned in *NumericAttributePtr, the driver ignores CharacterAttributePtr, BufferLength, and StringLengthPtr. When information is returned in *CharacterAttributePtr, the driver ignores NumericAttributePtr.
SQLColAttribute returns values from the descriptor fields of the IRD. The function is called with a statement handle, rather than a descriptor handle. The values returned by SQLColAttribute for the FieldIdentifier values listed later in this section can also be retrieved by calling SQLGetDescField with the appropriate IRD handle.
The currently defined descriptor fields, the version of ODBC in which they were introduced, and the arguments in which information is returned for them are shown later in this section; more descriptor types may be defined by drivers to take advantage of different data sources.
An ODBC 3.x driver must return a value for each of the descriptor fields. If a descriptor field does not apply to a driver or data source, then, unless otherwise stated, the driver returns 0 in *StringLengthPtr or an empty string in *CharacterAttributePtr.
The ODBC 3.x function SQLColAttribute replaces the deprecated ODBC 2.x function SQLColAttributes. When mapping SQLColAttributes to SQLColAttribute (when an ODBC 2.x application is working with an ODBC 3.x driver), or mapping SQLColAttribute to SQLColAttributes (when an ODBC 3.x application is working with an ODBC 2.x driver), the Driver Manager either passes the value of FieldIdentifier through, maps it to a new value, or returns an error, as follows:
Note The prefix used in FieldIdentifier values in ODBC 3.x has been changed from that used in ODBC 2.x. The new prefix is “SQL_DESC”; the old prefix was “SQL_COLUMN”.
The following table lists the descriptor types returned by SQLColAttribute.
FieldIdentifier |
Information returned in |
Description |
| SQL_DESC_AUTO_ UNIQUE_VALUE (ODBC 1.0) |
NumericAttributePtr | SQL_TRUE if the column is an autoincrementing column. SQL_FALSE if the column is not an autoincrementing column or is not numeric. This field is valid for numeric data type columns only. An application can insert values into a row containing an autoincrement column, but typically cannot update values in the column. When an insert is made into an auto-increment column, a unique value is inserted into the column at insert time. The increment is not defined, but is data-source – specific. An application should not assume that an auto-increment column starts at any particular point or increments by any particular value. |
| SQL_DESC_BASE_COLUMN_ NAME (ODBC 3.0) |
CharacterAttributePtr | The base column name for the result set column. If a base column name does not exist (as in the case of columns that are expressions), then this variable contains an empty string. This information is returned from the SQL_DESC_BASE_COLUMN_NAME record field of the IRD, which is a read-only field. |
| SQL_DESC_BASE_TABLE_ NAME (ODBC 3.0) |
CharacterAttributePtr | The name of the base table that contains the column. If the base table name cannot be defined or is not applicable, then this variable contains an empty string. This information is returned from the SQL_DESC_BASE_TABLE_NAME record field of the IRD, which is a read-only field. |
| SQL_DESC_CASE_SENSITIVE (ODBC 1.0) |
NumericAttributePtr | SQL_TRUE if the column is treated as case-sensitive for collations and comparisons. SQL_FALSE if the column is not treated as case-sensitive for collations and comparisons or is noncharacter. |
| SQL_DESC_CATALOG_NAME (ODBC 2.0) |
CharacterAttributePtr | The catalog of the table that contains the column. The returned value is implementation-defined if the column is an expression or if the column is part of a view. If the data source does not support catalogs or the catalog name cannot be determined, an empty string is returned. This VARCHAR record field is not limited to 128 characters. |
| SQL_DESC_CONCISE_TYPE (ODBC 1.0) |
NumericAttributePtr | The concise data type. For the datetime and interval data types, this field returns the concise data type; for examples, SQL_TYPE_TIME or SQL_INTERVAL_YEAR. (For more information, see “Data Type Identifiers and Descriptors” in Appendix D, “Data Types.”) This information is returned from the SQL_DESC_CONCISE_TYPE record field of the IRD. |
| SQL_DESC_COUNT (ODBC 1.0) |
NumericAttributePtr | The number of columns available in the result set. This returns 0 if there are no columns in the result set. The value in the ColumnNumber argument is ignored. This information is returned from the SQL_DESC_COUNT header field of the IRD. |
| SQL_DESC_DISPLAY_SIZE (ODBC 1.0) |
NumericAttributePtr | Maximum number of characters required to display data from the column. For more information about display size, see “Column Size, Decimal Digits, Transfer Octet Length, and Display Size” in Appendix D, “Data Types.” |
| SQL_DESC_FIXED_ PREC_SCALE (ODBC 1.0) |
NumericAttributePtr | SQL_TRUE if the column has a fixed precision and non-zero scale that are data-source – specific. SQL_FALSE if the column does not have a fixed precision and non-zero scale that are data-source – specific. |
| SQL_DESC_LABEL (ODBC 2.0) |
CharacterAttributePtr | The column label or title. For example, a column named EmpName might be labeled Employee Name, or might be labeled with an alias. If a column does not have a label, the column name is returned. If the column is unlabeled and unnamed, an empty string is returned. |
| SQL_DESC_LENGTH (ODBC 3.0) |
NumericAttributePtr | A numeric value that is either the maximum or actual character length of a character string or binary data type. It is the maximum character length for a fixed-length data type, or the actual character length for a variable-length data type. Its value always excludes the null-termination byte that ends the character string. This information is returned from the SQL_DESC_LENGTH record field of the IRD. For more information about length, see “Column Size, Decimal Digits, Transfer Octet Length, and Display Size” in Appendix D, “Data Types.” |
| SQL_DESC_LITERAL_PREFIX (ODBC 3.0) |
CharacterAttributePtr | This VARCHAR(128) record field contains the character or characters that the driver recognizes as a prefix for a literal of this data type. This field contains an empty string for a data type for which a literal prefix is not applicable. For more information, see “Literal Prefixes and Suffixes” in Chapter 8, “SQL Statements.” |
| SQL_DESC_LITERAL_SUFFIX (ODBC 3.0) |
CharacterAttributePtr | This VARCHAR(128) record field contains the character or characters that the driver recognizes as a suffix for a literal of this data type. This field contains an empty string for a data type for which a literal suffix is not applicable. For more information, see “Literal Prefixes and Suffixes” in Chapter 8, “SQL Statements.” |
| SQL_DESC_LOCAL_ TYPE_NAME (ODBC 3.0) |
CharacterAttributePtr | This VARCHAR(128) record field contains any localized (native language) name for the data type that may be different from the regular name of the data type. If there is no localized name, then an empty string is returned. This field is for display purposes only. The character set of the string is locale-dependent and is typically the default character set of the server. |
| SQL_DESC_NAME (ODBC 3.0) |
CharacterAttributePtr | The column alias, if it applies. If the column alias does not apply, the column name is returned. In either case, SQL_DESC_UNNAMED is set to SQL_NAMED. If there is no column name or a column alias, an empty string is returned and SQL_DESC_UNNAMED is set to SQL_UNNAMED. This information is returned from the SQL_DESC_NAME record field of the IRD. |
| SQL_DESC_NULLABLE (ODBC 3.0) |
NumericAttributePtr | SQL_ NULLABLE if the column can have NULL values; SQL_NO_NULLS if the column does not have NULL values; or SQL_NULLABLE_UNKNOWN if it is not known whether the column accepts NULL values. This information is returned from the SQL_DESC_NULLABLE record field of the IRD. |
| SQL_DESC_NUM_PREX_ RADIX (ODBC 3.0) |
NumericAttributePtr | If the data type in the SQL_DESC_TYPE field is an approximate numeric data type, this SQLINTEGER field contains a value of 2 because the SQL_DESC_PRECISION field contains the number of bits. If the data type in the SQL_DESC_TYPE field is an exact numeric data type, this field contains a value of 10 because the SQL_DESC_PRECISION field contains the number of decimal digits. This field is set to 0 for all non-numeric data types. |
| SQL_DESC_OCTET_LENGTH (ODBC 3.0) |
NumericAttributePtr | The length, in bytes, of a character string or binary data type. For fixed-length character or binary types, this is the actual length in bytes. For variable-length character or binary types, this is the maximum length in bytes. This value includes the null terminator. This information is returned from the SQL_DESC_OCTET_LENGTH record field of the IRD. For more information about length, see “Column Size, Decimal Digits, Transfer Octet Length, and Display Size” in Appendix D, “Data Types.” |
| SQL_DESC_PRECISION (ODBC 3.0) |
NumericAttributePtr | A numeric value that for a numeric data type denotes the applicable precision. For data types SQL_TYPE_TIME, SQL_TYPE_TIMESTAMP, and all the interval data types that represent a time interval, its value is the applicable precision of the fractional seconds component. This information is returned from the SQL_DESC_PRECISION record field of the IRD. |
| SQL_DESC_SCALE (ODBC 3.0) |
NumericAttributePtr | A numeric value that is the applicable scale for a numeric data type. For DECIMAL and NUMERIC data types, this is the defined scale. It is undefined for all other data types. This information is returned from the SCALE record field of the IRD. |
| SQL_DESC_SCHEMA_NAME (ODBC 2.0) |
CharacterAttributePtr | The schema of the table that contains the column. The returned value is implementation-defined if the column is an expression or if the column is part of a view. If the data source does not support schemas or the schema name cannot be determined, an empty string is returned. This VARCHAR record field is not limited to 128 characters. |
| SQL_DESC_SEARCHABLE (ODBC 1.0) |
NumericAttributePtr | SQL_PRED_NONE if the column cannot be used in a WHERE clause. (This is the same as the SQL_UNSEARCHABLE value in ODBC 2.x.) SQL_PRED_CHAR if the column can be used in a WHERE clause, but only with the LIKE predicate. (This is the same as the SQL_LIKE_ONLY value in ODBC 2.x.) SQL_PRED_BASIC if the column can be used in a WHERE clause with all the comparison operators except LIKE. (This is the same as the SQL_EXCEPT_LIKE value in ODBC 2.x.) SQL_PRED_SEARCHABLE if the column can be used in a WHERE clause with any comparison operator. Columns of type SQL_LONGVARCHAR and SQL_LONGVARBINARY usually return SQL_PRED_CHAR. |
| SQL_DESC_TABLE_NAME (ODBC 2.0) |
CharacterAttributePtr | The name of the table that contains the column. The returned value is implementation-defined if the column is an expression or if the column is part of a view. If the table name cannot be determined, an empty string is returned. |
| SQL_DESC_TYPE (ODBC 3.0) |
NumericAttributePtr | A numeric value that specifies the SQL data type. When ColumnNumber is equal to 0, SQL_BINARY is returned for variable-length bookmarks, and SQL_INTEGER is returned for fixed-length bookmarks. For the datetime and interval data types, this field returns the verbose data type: SQL_DATETIME or SQL_INTERVAL. (For more information, see “Data Type Identifiers and Descriptors” in Appendix D, “Data Types.”) This information is returned from the SQL_DESC_TYPE record field of the IRD. Note To work against ODBC 2.x drivers, use SQL_DESC_CONCISE_TYPE instead. |
| SQL_DESC_TYPE_NAME (ODBC 1.0) |
Character AttributePtr |
Data source – dependent data type name; for example, “CHAR”, “VARCHAR”, “MONEY”, “LONG VARBINARY”, or “CHAR ( ) FOR BIT DATA”. If the type is unknown, an empty string is returned. |
| SQL_DESC_UNNAMED (ODBC 3.0) |
Numeric AttributePtr |
SQL_NAMED or SQL_UNNAMED. If the SQL_DESC_NAME field of the IRD contains a column alias or a column name, SQL_NAMED is returned. If there is no column name or column alias, SQL_UNNAMED is returned. This information is returned from the SQL_DESC_UNNAMED record field of the IRD. |
| SQL_DESC_UNSIGNED (ODBC 1.0) |
Numeric AttributePtr |
SQL_TRUE if the column is unsigned (or not numeric). SQL_FALSE if the column is signed. |
| SQL_DESC_UPDATABLE (ODBC 1.0) |
Numeric AttributePtr |
Column is described by the values for the defined constants:
SQL_ATTR_READONLY SQL_DESC_UPDATABLE describes the updatability of the column in the result set, not the column in the base table. The updatability of the base column on which the result set column is based may be different from the value in this field. Whether a column is updatable can be based on the data type, user privileges, and the definition of the result set itself. If it is unclear whether a column is updatable, SQL_ATTR_READWRITE_UNKNOWN should be returned. |
This function is an extensible alternative to SQLDescribeCol. SQLDescribeCol returns a fixed set of descriptor information based on ANSI-89 SQL. SQLColAttribute allows access to the more extensive set of descriptor information available in ANSI SQL-92 and DBMS vendor extensions.
Related Functions
| For information about | See |
| Binding a buffer to a column in a result set | SQLBindCol |
| Canceling statement processing | SQLCancel |
| Returning information about a column in a result set | SQLDescribeCol |
| Fetching a block of data or scrolling through a result set | SQLFetchScroll |
| Fetching multiple rows of data | SQLFetch |