Short Question Answers
Q What do you mean by data dictionary ?
A A data dictionary is a file that contains "meta data" i.e data about data.
Q What are the main classification of SQL statements ?
A SQL commands are classifieds as follows
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Data Defination Language (DDL) - allows you to perform tasks related to data defination eg CREATE, ALTER, DROP
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Data Manipulation Langugae (DML)- enables users to access or manipulate data as organized by appropriate data model eg SELECT, INSERT, UPDATE
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Transaction Control Languages(TCL)- To manage and control transactions Transaction Control Language is used eg COMMIT, ROLLBACK, SAVEPOINT.
Q What do you mean by schema ?
A A schema refers to collection of logical structures of data. Schema
objects are logical structures that directly refer to the database's
data.
Q Name some schema objects ?
A Some of the schema objetcs are:-
Clusters - These are storage areas storing related tables and indexes.
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Database Triggers- These are stored subprograms associated with tables which are executed automatically .
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Indexes-
An index contains an entry for each value that appears in the indexed
column(s) of table or cluster. Index provides fast access to rows.
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Packages- A package is a collection of related procedures, functions and other program objetcs stored in the database.
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Stored Procedures- a group of PL/SQL statements that can be invoked or called from SQL or PL/SQL
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Tables - A table is a collection of related data.
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Views- a virtual table that draws data from existing table, but actually doesn't contain data , only maintains pointers.
