Oracle Built−in Packages- P81 potx

given pattern LOADFROMFILE Loads all or part of external LOB to internal LOB No READ Provides piece−wise read access to a LOB No SUBSTR Provides piece−wise read access to a LOB Yes TRIM Trims the contents of an internal LOB to the length specified by the newlenparameter No WRITE Writes a given number of bytes or characters to an internal LOB at a specified offset No Table Table 8.2 shows which LOB types you can manipulate with the individual DBMS_LOB programs. For an explanation of these LOB types, see the section Section 8.2, "LOB Concepts"" later in this chapter. Table 8.2: DBMS_LOB Programs Can Manipulate These LOB Types Program BFILE BLOB CLOB NCLOB APPEND X X X COMPARE X X X X COPY X X X ERASE X X X FILECLOSE X FILECLOSEALL X FILEEXISTS X FILEGETNAME X FILEISOPEN X FILEOPEN X GETLENGTH X X X X INSTR X X X X LOADFROMFILE X X X X READ X X X X SUBSTR X X X X TRIM X X X WRITE X X X [Appendix A] What's on the Companion Disk? 8. Managing Large Objects 391 8.1.2 DBMS_LOB Exceptions Table Table 8.3 summarizes the exceptions declared by DBMS_LOB. Table 8.3: DBMS_LOB Exceptions Exception SQLCODE Cause INVALID_ARGVAL −21560 DBMS_LOB expects a valid argument to be passed, but the argument was NULL or invalid. Example: FILEOPEN is passed an invalid open mode. Example: a positional or size argument is outside of the range 1 through (4 gigabytes−1). ACCESS_ERROR −22925 An attempt to read or write beyond maximum LOB size has occurred. NOEXIST_DIRECTORY −22285 The directory specified does not exist in the data dictionary. NOPRIV_DIRECTORY −22286 The user does not have the required privileges on either the specified directory object or the specified file. INVALID_DIRECTORY −22287 The directory specified is not valid or has been modified by the database administrator since the last access. OPERATION_FAILED −22288 An operation attempted on a file failed. UNOPENED_FILE −22289 An operation was performed on a file that was not open. OPEN_TOOMANY −22290 The maximum number of open files has been reached. This maximum is set via the SESSION_MAX_OPEN_FILES database initialization parameter. The maximum applies to many kinds of files, not only BFILES; for example, it applies to files opened using the UTL_FILE package. 8.1.3 DBMS_LOB Nonprogram Elements Table Table 8.4 summarizes the constants declared by the DBMS_LOB package. Table 8.4: DBMS_LOB Constants Element Name Type Value FILE_READONLY CONSTANT BINARY_INTEGER Zero. Mode used to open files. LOBMAXSIZE CONSTANT INTEGER 4,294,967,295 (4 gigabytes−1). Positional and size arguments cannot exceed this value. 8.1.4 About the Examples This chapter contains many examples of DBMS_LOB usage. For my examples, I use tables called my_book_files and my_book_text, which contain (or point to) large volumes of text for a book. The structures of these tables follow: /* Filename on companion disk: lobtabs.sql */* [Appendix A] What's on the Companion Disk? 8.1.2 DBMS_LOB Exceptions 392 CREATE TABLE my_book_files ( file_descr VARCHAR2(100), book_file BFILE); CREATE TABLE my_book_text ( chapter_descr VARCHAR2(100), chapter_text CLOB); Often, I'll query one of the fields from the table for a given chapter (chapter_desc) value. To avoid repetition of code, here are the implementations of functions that will be used throughout the examples: /* Filename on companion disk: lobfuncs.sql */* CREATE OR REPLACE FUNCTION book_file (chapter_in IN VARCHAR2) RETURN BFILE IS CURSOR book_cur IS SELECT book_file FROM my_book_files WHERE file_descr = chapter_in; book_rec book_cur%ROWTYPE; BEGIN OPEN book_cur; FETCH book_cur INTO book_rec; CLOSE book_cur; RETURN book_rec.book_file; END; / CREATE OR REPLACE FUNCTION book_text (chapter_in IN VARCHAR2) RETURN CLOB IS CURSOR book_cur IS SELECT chapter_text FROM my_book_text WHERE chapter_descr = chapter_in; book_rec book_cur%ROWTYPE; BEGIN OPEN book_cur; FETCH book_cur INTO book_rec; CLOSE book_cur; RETURN book_rec.chapter_text; END; / CREATE OR REPLACE FUNCTION book_text_forupdate (chapter_in IN VARCHAR2) RETURN CLOB IS CURSOR book_cur IS SELECT chapter_text FROM my_book_text WHERE chapter_descr = chapter_in FOR UPDATE; book_rec book_cur%ROWTYPE; BEGIN OPEN book_cur; FETCH book_cur INTO book_rec; CLOSE book_cur; RETURN book_rec.chapter_text; END; / In several of the examples, I'll compare before and after "images" of LOB content using the following statements (stored in the compare_text.sql file): [Appendix A] What's on the Companion Disk? 8.1.2 DBMS_LOB Exceptions 393 SELECT chapter_descr, chapter_text FROM my_book_text WHERE chapter_descr = '&1' ROLLBACK; EXEC DBMS_OUTPUT.PUT_LINE ('Rollback completed'); SELECT chapter_descr, chapter_text FROM my_book_text WHERE chapter_descr = '&1' END; / NOTE: It's a good practice to include exception handlers in any program working with LOBs to trap and deal with LOB−related errors. Not all of the programs and anonymous blocks shown in this chapter include exception handlers, but that is done only to reduce overall code volume. 7.3 DBMS_APPLICATION_INFO Examples 8.2 LOB Concepts Copyright (c) 2000 O'Reilly & Associates. All rights reserved. [Appendix A] What's on the Companion Disk? 8.1.2 DBMS_LOB Exceptions 394 Chapter 8 Managing Large Objects 8.2 LOB Concepts This section describes some basic LOB concepts you'll need to understand when you work with large objects. 8.2.1 LOB Datatypes Oracle8 provides four LOB datatypes: BFILE Large binary objects stored in operating system files outside of the database; for example, a bitmap image file. BLOB Large objects consisting of unstructured binary data. CLOB Large objects consisting of single−byte fixed−width character data. NCLOB Large binary objects consisting of single−byte or multiple−byte fixed−width character data. 8.2.1.1 Internal and external LOBs There are two categories of LOBs, depending upon their location with respect to the physical database: • Internal LOBs (of datatypes BLOB, CLOB, and NCLOB) are stored in the database and can participate in transactions. Changes to internal LOB values can be rolled back or committed. A cursor can select an internal LOB FOR UPDATE. Uncommitted changes to an internal LOB are not seen by a separate session. • External LOBs (of datatype BFILE) are stored outside of the database in operating system files and cannot participate in transactions. Instead, the underlying operating system provides the data integrity. Access to external LOBs is read−only. 8.2.1.2 The BFILE datatype The BFILE datatype is used to store large binary objects (up to four gigabytes) in files outside of the database. A BFILE could be a PL/SQL variable, DECLARE my_book_file BFILE; or a column in a table, 395 . LOB concepts you'll need to understand when you work with large objects. 8.2.1 LOB Datatypes Oracle8 provides four LOB datatypes: BFILE Large binary objects stored in operating system files