Oracle SQL Jumpstart with Examples- P3

Oracle SQL Jumpstart with Examples- P3: Review"As a consultant with more than 12 years of experience working with Oracle databases on a daily basis, reviewing this book was a unique and enjoyable experience. The SQL language is without doubt one of the most critical database skills and it is best learned by example. This book addresses that crucial need. Mr. Powell does an excellent job of clarifying the concepts by using meaningful and easy to understand examples. Frankly, I have not come across any other book on SQL that is as good a compilation of SQL concepts in a single...
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Oracle SQL Jumpstart with Examples- P3 70 3.5 Enhancing the Physical Architecture Figure 3.12 Oracle Standby/ Fail-over Database Architecture. safety can be transferred to a standby as they are created using the Log Writer (LGWR), filling a precreated archive log file on the standby data- base. On the other hand, maximum performance can be achieved at the expense of safety, thus potentially presenting possible data loss using the Archiver (ARCn) to transfer log entries from primary to standby. In this case, redo log entries are transferred when a primary database log switch occurs, copying each archive log file to a standby database as it is created. Using the Archiver, redo log entries are not copied as they are created but only after primary database archiving. Physical standby has disadvantages. A physical standby can only be accessed externally in read-only mode, and it must duplicate the source (primary) database exactly. A logical standby database is maintained in read-write mode, a completely open and accessible database. Also, a logical standby can have a subset of source database objects and can even contain objects in addition to the primary database. Once again, logical standby is much more flexible than physical standby. 3.5.5 Clustering and Oracle RAC Clustering was previously called Oracle Parallel Server and is now called Oracle Real Application Clusters (RAC). Oracle RAC allows for sharing of a single large data source’s data across more than one Oracle instance, run- ning on more than a single database server. Thus multiple database servers share the same data, allowing for high availability, enormous scalability, and flexibility.Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 3.5 Enhancing the Physical Architecture 71 So far, this book has examined the underlying logical and physical struc- ture of Oracle Database plus new features available in both Oracle Database 10g and Oracle Database 9i. Now it’s time to begin looking into Oracle SQL itself. The next chapter begins this process by examining the SELECT statement. Chapter 3Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. This page intentionally left blankPlease purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 4 The SELECT Statement In this chapter: How do you write a basic query using SELECT statements? What types of SELECT statements are possible? What else is interesting about SELECT statements? In this chapter, we dive right into the syntax and use of the SELECT statement to query the database. We also briefly discuss different types of queries, finally examining specific aspects of queries such as using DIS- TINCT and the DUAL table. So let’s begin with the basics of the SELECT statement and some simple examples just to get into the swing of things. 4.1 The Basic SELECT Statement SELECT is the beginning of the SQL command for querying (retrieving) data from a database table, view, or object. Objects are similar to tables, but they have a more complex structure. 4.1.1 Uses of the SELECT Statement The SELECT statement is a specialized way to ask a question about the data in a database. Thus a SELECT statement is also called a query because it quite literally “queries” or asks questions of a database. There are several uses for the SELECT statement that give you great flexibility in the database: ...