input output利用Oracle存取文件——输入输出解析（oraclefile）

When interacting with files, most programs need to be able to read and write to the file system. This is done with input/output (IO) operations. In Oracle, there are a variety of ways to access files.

The most common way is to use Oracle Directories. This is a feature of Oracle Database where you can store files on the server and refer to them as directory objects. Oracle Directories provide a secure and portable way of accessing files and can be used to store any type of file type, including text, images, binary files, and more.

You can also use the UTL_FILE and DBMS_LOB packages in Oracle to read and write files. UTL_FILE is a built-in Oracle package that allows you to read and write files from the database server. The DBMS_LOB package provides an interface to read and write large objects (LOBs), such as images and documents.

In addition to the two packages, Oracle also provides special SQL functions for dealing with files. These functions enable you to read and write files using SQL statements.

For example, you can use the following statement to read a text file on the database server:

SELECT UTL_FILE.get_raw(‘MYDIR’,’myfile.txt’)
FROM dual;

The statement returns the contents of the file as raw data.

You can use the same statement to write a file to the database server:

BEGIN
 UTL_FILE.PUT_RAW(‘MYDIR’,’myfile.txt’,’This is the contents of my file.’);
END;

You can also use the special SQL functions to create and delete directories or list all the files in the directory:

BEGIN
  UTL_FILE.CREATE_DIR(‘MYDIR’);
END;
BEGIN
  UTL_FILE.DELETE_DIR(‘MYDIR’);
END;

SELECT UTL_FILE.dir_listdir(‘MYDIR’);

Overall, Oracle provides a number of ways to read and write files on the database server. By leveraging the built in packages, such as UTL_FILE and DBMS_LOB, it is possible to easily perform IO operations with the database. In addition, the special SQL functions enable you to quickly create and delete directories, list all the files in the directory, and more.