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Introduction to Oracle UtilitiesOracle's database utilities let you perform the following tasks:- High-speed movement of data and metadata from one database to another using Data Pump Export and Import- Extract and manipulate complete representations of the metadata for database objects, using t 阅读全文
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Introduction to Client/Server Architecture
In the Oracle database system environment, the database application and the database are separated into two parts: afront-end or client portion, and a back-end or server portion--hence the term client/server architecture. The client runs the database application that accesses database information and interacts with a user through the keyboard, screen, and pointing device, such as a mouse. The server runs the Oracle software and handles the functions 阅读全文
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All connected Oracle users must run two modules of code to access an Oracle database instance.
- Application or Oracle tool: A database user runs a database application (such as a precompiler program) or an Oracle tool (such as SQL*Plus), which issues SQL statements to an Oracle database.
- Oracle database server code: Each user has some Oracle database code executing on his or her behalf, which interprets and processes the application's SQL statements. 阅读全文
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The basic memor structures associated with Oracle include:
- System Global Area (SGA), which is shared by all server and background processes.
- Program Global Areas (PGA), which is private to each server and background process; there is on PGA for each process. 阅读全文
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One of the most important parts of an Oracle database is its data dictionary, which is a ready-only set of tables that provides information about the database. A data dictionary contains:
- The definitions of all schema objects in the database (tables, views, indexes, clusters, synonyms, sequences, procedures, functions, packages, triggers, and so on)
- How much space has been allocated for, and is currently used by, the schema objects.
- Default values for columns
- The names of Oracle user 阅读全文
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A schema is a collection of logical structures of data, or schema objects. A schema is owned by database user and has the same name as that user. Each User owns a single schema. Schema objects can be created and manipulated with SQL and include the following types of objects: Clusters; Database link 阅读全文
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A transaction is a logical unit of work that contains one or more SQL statements. A transaction is an atomic unit. The effects of all the SQL statements in a transaction can be either all committed (applied to the database) or all rolled back (undone from the database).
A transaction begins with the first executable SQL statement. A transaction ends when it is committed or rolled back, either explicitly with a COMMIT or ROLLBACK statement or implicitly when a DDL statement is issued. 阅读全文
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Oracle stores data locically in tablespaces and physically in datafiles associated with the corresponding tablespace. 阅读全文
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Oracle allocates logical database space for all data in a database. The units of database space allocation are data blocks, extents, and segments 阅读全文
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Oracle includes datatypes to handle all the types of rich Internet content such as relational data, object-relational data, XML, text, audio, video, image, and spatial. These datatypes appear as native types in the database. They can all be queried using SQL. A single SQL statement can include data beloging to any all of these datatypes. 阅读全文