Oracle PL/SQL Programming, Third Editionby Steven Feuerstein, Bill Pribyl
Nearly a quarter-million PL/SQL programmersnovices and experienced developers alikehave found the first and second editions of Oracle PL/SQL Programming to be indispensable references to this powerful language. Packed with examples and recommendations, this book has helped everyone, from Oracle Forms developers to database administrators, make/i>
Nearly a quarter-million PL/SQL programmersnovices and experienced developers alikehave found the first and second editions of Oracle PL/SQL Programming to be indispensable references to this powerful language. Packed with examples and recommendations, this book has helped everyone, from Oracle Forms developers to database administrators, make the most of PL/SQL. This new edition is a comprehensive update of the original book, covering all versions of PL/SQL through Oracle9i Release 2. It adds much-requested new chapters on how to create and run PL/SQL programs, call Java methods from within PL/SQL, and define and use database triggers. An extensive new chapterdesigned especially for experienced PL/SQL developersdescribes PL/SQL's runtime architecture and how to use knowledge of Oracle internals to get the best performance from PL/SQL.The book contains information about the latest Oracle9i PL/SQL features, including:
- Record-based DML: You can now use records in INSERT and DELETE statements.
- Table functions: These are functions that return a result set (in the form of a PL/SQL collection). Such functions existed in Oracle8i but they are now much expanded.
- New and improved datatypes: Oracle now offers dramatically improved support for timestamps, time zone management, and interval calculations. In addition, the XMLType datatype has now been implemented.
- Inheritance for object types: You can now define a hierarchy of object types (which were first introduced in Oracle8).
- Enhancements to PL/SQL collections. PL/SQL now supports multiple-level collections (nesting collections withincollections), as well as associative arrays (previously called index-by tables), which allow you to index by PLS_INTEGER and VARCHAR2.
- Native compilation of PL/SQL code: PL/SQL source code can now optionally be compiled into native object code that is linked into Oracle.
- Part I, Programming in PL/SQL
- Part II, PL/SQL Program Structure
- Part III, PL/SQL Program Data
- Part IV, SQL in PL/SQL
- Part V, PL/SQL Application Construction
- Part VI, Advanced PL/SQL Topics
- O'Reilly Media, Incorporated
- Publication date:
- Edition description:
- Third Edition
- Product dimensions:
- 7.02(w) x 9.32(h) x 1.65(d)
Read an Excerpt
From Chapter: Variables and Program Data
...The LONG datatype
A variable declared LONG can store variable-length strings of up to 32760 bytes--this is actually seven fewer bytes than allowed in VARCHAR2 type variables! The LONG datatype for PL/SQL variables is quite different from the LONG datatype for columns in the Oracle Server. The LONG datatype in Oracle7 can store character strings of up to two gigabytes or 231-1 bytes; this large size makes the LONG column a possible repository of mulitmedia information, such as graphics images.
As a result of these maximum length differences, you can always insert a PL/SQL LONG variable value into a LONG database column, but you cannot select a LONG database value larger than 32760 bytes into a PL/SQL LONG variable.
In the Oracle database, there are many restrictions on how the LONG column can be used in a SQL statement; for example:
- A tale may not contain more than one single LONG column.
- Yoiu may not use the LONG column in a GROUP BY, ORDER BY, WHERE, or CONNECT BY clause.
- You may not apply character functions (such as SUBSTR, INSTR, or LENGTH), to the LONG column.
Given the fact that aVARCHAR2 variable actually has a higher maximum length than the LONG and has no restrictions attached to it, I recommend that you always use the VARCHAR2 datatype in PL/SQL programs. LONGs have a place in the RDBMS, but that role is not duplicated in PL/SQL. This makes some sense since you will very rarely want to manipulate truly enormous strings within your program using such functions as SUBSTR or LENGTH or INSTR.
The RAW datatype
The RAW datatype is used to store binary data or other kinds of raw data, such as a digitized picture or image. A RAW variable has the same maximum length as VARCHAR2 (32767 bytes), which must also be specified when the variable is declared. The difference between RAW and VARCHAR2 is that PL/SQL will not try to interpret raw data. Within the Oracle RDBMS this means that Oracle will not perform character set conversions on RAW data when it is moved from one system (based, for example, on 7-bit ASCII) to another system.
Once again, there is an inconsistency between the PL/SQL maximum length for a RAW variable (32767) and the RDBMS maximum length (255). As a result, you cannot insert more than 255 bytes of your PL/SQL RAW variable's value into a database column. You can, on the other hand, insert the full value of a PL/SQL RAW variable into a column with type LONG RAW, which is a two-gigabyte container for raw data in the database.
The LONG RAW datatype
The LONG RAW datatype stores raw data of up to 32760 bytes and is just like the LONG datatype excerpt that the data in a LONG RAW variable is not interpreted by PL/SQL.
Given the fact that a RAW variable actually has a higher maximum length than the LONG RAW and has no restrictions attached to it, I recommended that you always use the RAW datatype in PL/SQL programs. LONG RAWs have a place in the RDBMS, but that role is not duplicated in PL/SQL.
The ROWID datatype
In the Oracle RDBMS, ROWID is a pseudocolumn that is part of every table you create. the rowid is an internally generated and maintained binary value which identifies a row of data in your table. It is called a pseudocolumn because a SQL statement includes it in places where you would normally use a column. However, it is not a column that you create for the table. Instead, the RDBMS generates the rowid for each row as it is inserted into the database. The information in the rowid provides the exact physical location of the row in the database. You cannot change the value of a rowid.
You can use the ROWID datatype to store rowids from the database in your PL/SQL program. You can SELECT or FETCH the rowid for a row into a ROWID variable. To manipulate rowids in Oracle8, you will want to use the built-in package, DBMS_ROWID (see Appendix C, Built-In Packages). In Oracle7, you will use the ROWIDTOCHAR function to convert the rowid to a fixed-length string and then perform operations against that string.
In Oracle7, for format of the fixed-length rowid is as follows:
Components of this format have the following meanings:
The block in the database file
The row in the clock (where the first row is zero, not one)
The database file
All these numbers are hexadecimal; the database file is a number which you would then use to look up the actual name of the database file through the data dictionary.
In Oracle8, rowid have been "extended" to support partitioned tables and indexes. The new, extended rowids include a data object number, identifying the database segment. Any schema object found in the same segment, such as a cluster of tables, will have the same object number. In Oracle8, then, a rowid contains the following information:
- The data object number
- The data file (where the first file is 1)
- The data block within the data file
- The row in the data block (where the first row is 0)
Meet the Author
Steven Feuerstein is considered one of the world's leading experts on the Oracle PL/SQL language. He is the author or coauthor of Oracle PL/SQL Programming, Oracle PL/SQL Best Practices, Oracle PL/SQL Programming: Guide to Oracle8i Features, Oracle PL/SQL Developer's Workbook, Oracle Built-in Packages, Advanced Oracle PL/SQL Programming with Packages, and several pocket reference books (all from O'Reilly & Associates). Steven is a Senior Technology Advisor with Quest Software, has been developing software since 1980, and worked for Oracle Corporation from 1987 to 1992.
Bill Pribyl, author, teacher, and software consultant,is the primary author of Learning Oracle PL/SQL and the coauthor of Oracle PL/SQL Programming and its companion pocket reference, all published by O'Reilly & Associates. An Oracle user since 1986, Bill has consulted on many aspects of using Oracle products. He recently spearheaded PLNet.org, a Web-based repository where developers can share open source PL/SQL.
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