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

SAS/ACCESS Interface to Microsoft SQL Server 4 Naming Conventions for Microsoft SQL Server 601Isolation LevelRU (read uncommitted)V (versioning)DefinitionAllows dirty reads, nonrepeatable reads, and phantomreads.Does not allow dirty reads, nonrepeatable reads, orphantom reads. These transactions are serializable buthigher concurrency is possible than with the serializableisolation level. Typically, a nonlocking protocol is used.Here is how the terms in the table are defined.Dirty readNonrepeatablereadPhantom readsA transaction that exhibits this phenomenon has very minimalisolation from concurrent transactions. In fact, the transactioncan see changes that are made by those concurrenttransactions even before they commit.For example, if transaction T1 performs an update on a row,transaction T2 then retrieves that row, and transaction T1 thenterminates with rollback. Transaction T2 has then seen a rowthat no longer exists.If a transaction exhibits this phenomenon, it is possible that itmight read a row once and, if it attempts to read that rowagain later in the course of the same transaction, the row mighthave been changed or even deleted by another concurrenttransaction. Therefore, the read is not necessarily repeatable.For example, if transaction T1 retrieves a row, transactionT2 updates that row, and transaction T1 then retrieves thesame row again. Transaction T1 has now retrieved the samerow twice but has seen two different values for it.When 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, transaction T1 retrieves the set of all rows thatsatisfy some condition. If transaction T2 inserts a new row thatsatisfies that same condition and transaction T1 repeats itsretrieval request, it sees a row that did not previously exist, aphantom.UPDATE_ISOLATION_LEVEL= S | RR | RC | VThe Microsoft SQL Server ODBC driver manager supports the S, RR, RC, and Visolation levels that are defined in the preceding table.Naming Conventions for Microsoft SQL ServerFor general information about this feature, see Chapter 2, “SAS Names and Supportfor DBMS Names,” on page 11.The PRESERVE_COL_NAMES= and PRESERVE_TAB_NAMES= LIBNAME optionsdetermine how SAS/ACCESS Interface to Microsoft SQL Server handles case sensitivity,spaces, and special characters. (For information about these options, see “Overview ofthe LIBNAME Statement for Relational Databases” on page 87.) The default value forboth of these options is YES for Microsoft Access, Microsoft Excel, and Microsoft SQL