SAS/ACCESS 9.2 for Relational Databases: Reference, Fourth Edition

The ACCESS Procedure for Relational Databases 4 Access Descriptors 907Altering a DBMS table might invalidate descriptor files that are based on the DBMStable, or it might cause these files to be out of date. If you re-create a table, add a newcolumn to a table, or delete an existing column from a table, use the UPDATEstatement to modify your descriptors so that they use the new information.Rules that apply to the CREATE statement also apply to the UPDATE statement.For example, the SUBSET statement is valid only for updating view descriptors.The following statements are not supported when you use the UPDATE statement:ASSIGN, RESET, SELECT, and UNIQUE.See Table A1.1 on page 894 for the appropriate sequence of statements for updatingdescriptors.Using Descriptors with the ACCESS ProcedureWhat Are Descriptors?Descriptors work with the ACCESS procedure by providing information about DBMSobjects to SAS, enabling you to access and update DBMS data from within a SASsession or program.There are two types of descriptors, access descriptors and view descriptors. Accessdescriptors provide SAS with information about the structure and attributes of a DBMStable or view. An access descriptor, in turn, is used to create one or more viewdescriptors, or SAS data views, of the DBMS data.Access DescriptorsTypically, each DBMS table or view has a single access descriptor that providesconnection information, data type information, and names for databases, tables, andcolumns.You use an access descriptor to create one or more view descriptors. When creating aview descriptor, you select the columns and specify criteria for the rows you want toretrieve. The figure below illustrates the descriptor creation process. Note that anaccess descriptor, which contains the metadata of the DBMS table, must be createdbefore view descriptors can be created.