Introduction and use of Oracle Data Dictionary

Oracle data dictionary introduction and use of Chinese name: data dictionary English name: data dictionary Definition: a set of information about all objects in the database and their relationships. A Data Dictionary defines and describes data items, data structures, data streams, data storage, processing logic, and external entities, the purpose is to give a detailed description of each element in the data flow chart. The www.2cto.com Data dictionary is a directory that you can access to record database and application source Data. An active data dictionary is a data dictionary that can be automatically updated by the DBMS when the database or application structure is modified. A passive data dictionary is a data dictionary that must be updated manually when being modified. A data dictionary is a reserved space and a database, which is used to store the information database itself. Information that a data dictionary may contain, for example: database Design Data Storage SQL program User Permissions user statistics information database growth statistics database performance statistics dictionary is a collection of various types of data descriptions in the system, is the main result of detailed data collection and data analysis. A data dictionary consists of data items, data structures, data streams, and data storage and processing processes. Data items are the smallest component of data. Several data items can constitute a data structure. data dictionaries describe the logical content of data streams and data storage by defining data items and data structures. A data dictionary is a set of data information, that is, a set of definitions of all elements contained in a data flow diagram. data Dictionary also has another meaning. It is a tool used in Database Design to describe the design of basic tables in the database, it mainly includes the field name, data type, primary key, foreign key, and so on. The most important role of data dictionary is as a tool in the analysis phase. The most important purpose of any dictionary is to explain the items that people do not understand. In structural analysis, the role of a data dictionary is to define and describe each component in a data flow chart. In other words, the text set of the definition and interpretation of all the components in the data flow chart is the data dictionary, and a set of closely consistent definitions established in the data dictionary helps improve the communication between analysts and users. Data Dictionary composition: 1. Data Item 2. Data Structure 3. Data Stream 4. Data Storage 5. Data Dictionary during processing is an important part of the database. It stores the information used by the database. for users, it is a set of read-only tables. Data Dictionary content includes: 1. Information about all schema objects in the database, such as tables, views, clusters, and indexes. 2. How much space is allocated and how much space is currently used. 3. Column default value. 4. Constraints on the integrity of information. 5. User Name. 6. permissions granted to users and roles. 7. Audit information accessed or used by the user. 8. Other generated database information. A database data dictionary is a group of tables and view structures. They are stored in the SYSTEM tablespace. The database data dictionary is not only the center of each database. It is also very important to every user. You can use SQL statements to access the database data dictionary. A collection of data information is a directory that allows users to access and record database and application metadata, it refers to the physical and logical description of the table information in the database. The data dictionary is a group of tables and view structures. They are stored in the SYSTEM tablespace. Database Data dictionary is not only the center of each database, but also very important information for each user. You can use SQL statements to access the database data dictionary. A data dictionary is a set of data information, that is, a set of definitions of all elements contained in a data flow diagram. Composition: 1. Data items: a data item is the most basic data element and the smallest meaningful data unit. In a data dictionary, data items are defined as follows: data item name, number, alias, and description; data item length; data item value range. 2. Data Structure: data items cannot be decomposed, while data structures are data packets that can be further decomposed. A data structure consists of two or more correlated data elements or other data structures. A data structure can be composed of several data elements, several data structures, and several data elements and data structures. 3. Data Stream: a data stream consists of one or more fixed data items. When defining a data stream, it not only describes the name and composition of the data stream, but also specifies its source, destination, and data traffic. 4. Data Storage: data is stored in a data dictionary and only describes the logical storage structure of data, without involving its physical organization. 5. processing process: the definition of processing logic only describes the bottom-layer logic in the data flow chart. Select * from dictionary; a data dictionary is used to describe data when Oracle stores database information. For example, the Creator information, creation time information, tablespace information, and user access permission information of a table. A database data dictionary is a group of tables and view structures. They are stored in the SYSTEM tablespace. When users encounter difficulties in operating the data in the database, they can access the data dictionary to view detailed information. You can use SQL statements to access the database data dictionary. Data Dictionary content includes: 1. Information about all schema objects in the database, such as tables, views, clusters, and indexes. 2. How much space is allocated and how much space is currently used. 3. Column default value. 4. Constraints on information integrity. 5. Oracle user name. 6. permissions granted to users and roles. 7. Audit information accessed or used by the user. 8. Other generated database information. Data dictionaries in Oracle are static and dynamic. 1. static data dictionary --> it does not change when users access the data dictionary. For example, table 2 created by a user, A Dynamic Data Dictionary depends on the performance of the database and reflects some internal information about the database operation. Therefore, it is not always the same when accessing such data dictionaries. -- Currently locked object static data dictionary: This type of data dictionary is mainly composed of tables and views. Tables in the data dictionary cannot be directly accessed, but can access the views in the data dictionary. The views in the static data dictionary are divided into three types, which have three prefixes: user _ *, all _ *, and dba _*. User _ * this view stores information about the objects owned by the current user. (That is, all objects in this user mode) all _ * indicates the object information that the current user can access. (Compared with user _ *, all _ * does not need to own this object. You only need to have the permission to access this object.) dba _ * this view stores information about all objects in the database. (The premise is that the current user has the permission to access these databases and generally must have the Administrator permission) Explain select * from dictionary; -- query the tables owned by the user -- user_tables mainly describes information about all the tables owned by the current user, including the table name, tablespace name, and cluster name. Through this view, you can clearly understand which desc user_tables; select table_name from user_tables; select * from user_tables; -- query the indexes owned by this user select index_name from user_indexes; -- query the views owned by the user. select view_name from user_views; -- query the database objects owned by the user, objects include tables, views, stored procedures, triggers, packages, indexes, sequences, and JAVA files. Select object_name from user_objects; -- mainly describes the information of the current user, including the current user name, account id, account status, tablespace name, and creation time. Select * from user_users; Difference -- user _/all _ difference: ---- all _ indicates the objects that the current user can access, rather than the objects owned by the current user. -- Query all tables, processes, and functions of a user. Select owner, object_name, object_type from all_objects tables -- administrator permission is required for dba _ and table space information is queried (the current user must have the DBA role ). Select * from dba_data_files history the dynamic data dictionary Oracle contains some potential tables and views maintained by system administrators, such as SYS. Since these tables and views are constantly updated when the database is running, therefore, they are called dynamic data dictionaries (or dynamic performance views ). These views provide information about the memory and disk operations, so we can only read-only access them, but not modify them. In Oracle, these dynamic performance views are all views starting with v $. v $ access. This view displays the database objects locked in the database and the session objects (session objects) that access these objects ). Select * from v $ access v $ session this view lists the details of the current session. V $ active_instance this view mainly describes the information of active instances in the current database. You can still use the select statement to observe this information. V $ context this view lists the attributes of the current session. For example, namespace and attribute value