发行说明

40.4 ADT 变换

以下内容会取代本书中的现有信息。

• There is a new descriptor type (smallint) SQL_DESC_USER_DEFINED_TYPE_CODE, with values:

     SQL_TYPE_BASE 0	(this is not a USER_DEFINED_TYPE)
     SQL_TYPE_DISTINCT 1	 
     SQL_TYPE_STRUCTURED	2 
     This value can be queried with either SQLColAttribute
       or SQLGetDescField (IRD only).
   
     The following attributes are added to obtain the actual type names:
    	SQL_DESC_REFERENCE_TYPE
    	SQL_DESC_STRUCTURED_TYPE
    	SQL_DESC_USER_TYPE 
     The above values can be queried using SQLColAttribute
       or SQLGetDescField (IRD only).
  

• Add SQL_DESC_BASE_TYPE in case the application needs it. For example, the application may not recognize the structured type, but intends to fetch or insert it, and let other code deal with the details.
• Add a new connection attribute called SQL_ATTR_TRANSFORM_GROUP to allow an application to set the transform group (rather than use the SQL "SET CURRENT DEFAULT TRANSFORM GROUP" statement).
• Add a new statement/connection attribute called SQL_ATTR_RETURN_USER_DEFINED_TYPES that can be set or queried using SQLSetConnectAttr, which causes CLI to return the value SQL_DESC_USER_DEFINED_TYPE_CODE as a valid SQL type. This attribute is required before using any of the transforms.
  • By default, the attribute is off, and causes the base type information to be returned as the SQL type.
  • When enabled, SQL_DESC_USER_DEFINED_TYPE_CODE will be returned as the SQL_TYPE. The application is expected to check for SQL_DESC_USER_DEFINED_TYPE_CODE, and then to retrieve the appropriate type name. This will be available to SQLColAttribute, SQLDescribeCol, and SQLGetDescField.
• The SQLBindParameter does not give an error when you bind SQL_C_DEFAULT, because there is no code to allow SQLBindParameter to specify the type SQL_USER_DEFINED_TYPE. The standard default C types will be used, based on the base SQL type flowed to the server. For example:

     sqlrc = SQLBindParameter (hstmt, 2, SQL_PARAM_INPUT, SQL_C_CHAR, SQL_VARCHAR, 30,
                                                    0, &c2, 30, NULL);