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分类: Oracle

2006-11-28 18:22:11

1.Logical Database Structures
The logical structures of an Oracle database include schema objects, data blocks,extents, segments, and tablespaces.
2.Oracle tablespace
(There is no relationship between a tablespace and a schema.Objects in the same schema can be in different tablespaces, and a tablespace can hold objects from different schemas.)
3.Oracle stores
each row of a database table containing data for less than 256 columns as one or more row pieces.
4.Views & Indexes
Views do not actually contain data.Like tables, views can be queried, updated, inserted into, and deleted from, with some restrictions. All operations performed on a view actually affect the base tables of the view.
Indexes are useful when applications frequently query a table for a range of rows (for example, all employees with a salary greater than 1000 dollars) or a specific row.
5.Segment
For a partitioned table, each partition has a data segment.Each cluster has a data segment. The data of every table in the cluster is stored in the cluster’s data segment.
For a partitioned index, each partition has an index segment.
6.Datafile
Data in a datafile is read, as needed, during normal database operation and stored in the memory cache of Oracle. For example, assume that a user wants to access some data in a table of a database. If the requested information is not already in the memory cache for the database, then it is read from the appropriate datafiles and stored in memory.
7.Controlfile
If the physical makeup of the database is altered (for example, if a new datafile or redo log file is created), then the control file is automatically modified by Oracle to reflect the change.
8.SQL*Loader
SQL*Loader accepts input data in a variety of formats, performs filtering (selectively loading records based on their data values), and loads data into multiple Oracle database tables during the same load session.
9.SQL
SQL statements are divided into the following categories:                        
 Data Definition Language (DDL) Statements: create, alter, maintain, and drop schema objects.also include statements that permit a user to grant other users the privileges to access the database and specific objects within the database.            
 Data Manipulation Language (DML) Statements: Locking a table or view and examining the execution plan of an SQL statement are alsoDML operations.                                             
 Transaction Control Statements:They enable a user to group changes into logical transactions.                                                            
 Session Control Statements:including enabling and disabling roles and changing language settings. The two session control statements are ALTER SESSION and SET ROLE                            
 System Control Statements:The only system control statement is ALTER SYSTEM.                             
 Embedded SQL Statements
10.Procedures&functions
Procedures and functions are identical, except that functions always return a single value to the user. Procedures do not return values.
                        
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