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

SAS/ACCESS Interface to Sybase IQ 4 Naming Conventions for Sybase IQ 775For example, suppose that transaction T1 performs anupdate on a row, transaction T2 then retrieves that row, andtransaction T1 then terminates with rollback. Transaction T2has then seen a row that no longer exists.NonrepeatablereadsIf a transaction exhibits this phenomenon, it is possible that itmight read a row once and if it attempts to read that row againlater in the course of the same transaction, the row might havebeen changed or even deleted by another concurrenttransaction. Therefore, the read is not (necessarily) repeatable.For example, suppose that transaction T1 retrieves a row,transaction T2 then updates that row, and transaction T1 thenretrieves the same row again. Transaction T1 has now retrievedthe same row twice but has seen two different values for it.Phantom readsWhen a transaction exhibits this phenomenon, a set of rowsthat it reads once might be a different set of rows if thetransaction attempts to read them again.For example, suppose that transaction T1 retrieves the set ofall rows that satisfy some condition. Suppose that transactionT2 then inserts a new row that satisfies that same condition. Iftransaction T1 now repeats its retrieval request, it sees a rowthat did not previously exist, a phantom.UPDATE_ISOLATION_LEVEL= S | RR | RCSybase IQ supports the S, RR, and RC isolation levels defined in the precedingtable.Naming Conventions for Sybase IQFor general information about this feature, see Chapter 2, “SAS Names and Supportfor DBMS Names,” on page 11.Since SAS 7, most SAS names can be up to 32 characters long. SAS/ACCESSInterface to Sybase IQ supports table names and column names that contain up to 32characters. If DBMS column names are longer than 32 characters, they are truncatedto 32 characters. If truncating a column name would result in identical names, SASgenerates a unique name by replacing the last character with a number. DBMS tablenames must be 32 characters or less because SAS does not truncate a longer name. Ifyou already have a table name that is greater than 32 characters, it is recommendedthat you create a table view. For more information, see Chapter 2, “SAS Names andSupport for DBMS Names,” on page 11.The PRESERVE_COL_NAMES= and PRESERVE_TAB_NAMES= options determinehow SAS/ACCESS Interface to Sybase IQ handles case sensitivity. (For informationabout these options, see “Overview of the LIBNAME Statement for RelationalDatabases” on page 87.) Sybase IQ is not case sensitive, so all names default tolowercase.Sybase IQ objects include tables, views, and columns. They follow these namingconventions.3 A name must be from 1 to 128 characters long.3 A name must begin with a letter (A through Z), underscore (_), at sign (@), dollarsign ($), or pound sign (#).3 Names are not case sensitive. For example, CUSTOMER and Customer are thesame, but object names are converted to lowercase when they are stored in the