SQL stands for structured
query language. It is used to communicate with the database. Whenever
any data is to be accessed from the database, we can do it through
the SQL, and user can access the required data from the database, can
manipulate data, can define the data in the database through SQL. SQL is a standard language for accessing databases.
SQL
is supposed as structured query language for relational database
management systems (RDBMS). SQL uses the combination of relational
algebra and relational calculus constructs. It has many other
capabilities besides querying the database. It includes the features
of defining the structure of the data, for modifying data in the
database and for specifying security constraints.
SQL has established
as standard relational database language, and its original version
was developed at IBM's San Jose Research Laboratory. It is also
called SEQUEL and was implemented as part of the system R project.
The purpose of this project was to validate the feasibility of
relational model and to implement a DBMS based on this model. The
results of this project are well documented in database literature.
Additionally, to contributing to the concept of query compilation and
optimization and concurrency control mechanisms, the most salient
result of this project was the development of SQL. SQL is a
nonprocedural language. Users describe in SQL what they want to do
and the SQL language compiler automatically generates a procedure to
navigate the database and performs the desired task.
Different parts of SQL
- Data Definition Language: It provides the commands for defining relation schemas, deleting relations, creating indices and modifying relation schemas.
- Data Manipulation Language: It includes a query language based on both the relational algebra and the tuple relational calculus. It also provides commands to insert, delete, and modify tuples in the database.
- View Definition: It includes commands for defining views.
- Transaction Control: It includes commands for specifying the beginning and ending of transactions.
- Integrity: The SQL DDL provides commands, for specifying integrity constraints, that the data stored in the database irriust satisfy. Updates that can violate integrity constraints are disallowed.
- Authorization: The SQL DDL provides commands for specifying access rights to relations and views.
- Embedded SQL and Dynamic SQL: Embedded and dynamic SQL define how SQL statements are embedded within programming languages such as C, C++, Java.
Posts
0 comments:
Post a Comment