Overview of the SQL Query Language

IBM developed the original version of SQL, originally called Sequel, as part of the
System R project in the early 1970s. The Sequel language has evolved since then,
and its name has changed to SQL (Structured Query Language). Many products
now support the SQL language. SQL has clearly established itself as the standard
relational database language.

In 1986, the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO) published an SQL standard, called
SQL-86. ANSI published an extended standard for SQL, SQL-89, in 1989. The next version of the standard was SQL-92 standard, followed by SQL:1999, SQL:2003, SQL:2006, and most recently SQL:2008. The bibliographic notes provide references to these standards.

The SQL language has several parts:

Data-definition language (DDL): The SQL DDL provides commands for defin?ing relation schemas, deleting relations, and modifying relation schemas.

Data-manipulation language (DML): The SQL DML provides the ability to
query information from the database and to insert tuples into, delete tuples
from, and modify tuples in the database.

Integrity: The SQL DDL includes commands for specifying integrity con?straints that the data stored in the database must satisfy. Updates that violate
integrity constraints are disallowed.

View definition: The SQL DDL includes commands for defining views.

Transaction control: SQL includes commands for specifying the beginning
and ending of transactions.

Embedded SQL and dynamic SQL: Embedded and dynamic SQL define how
SQL statements can be embedded within general-purpose programming languages, such as C, C++, and Java.

Authorization: The SQL DDL includes commands for specifying access rights
to relations and views.


Frequently Asked Questions

Ans: An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches. view more..
Ans: All procedural relational query languages provide a set of operations that can be applied to either a single relation or a pair of relations. view more..
Ans: A query language is a language in which a user requests information from the database. view more..
Ans: IBM developed the original version of SQL, originally called Sequel, as part of the System R project in the early 1970s. view more..
Ans: The set of relations in a database must be specified to the system by means of a data-definition language (DDL). view more..
Ans: The basic structure of an SQL query consists of three clauses: select, from, and where. view more..
Ans: This chapter discusses techniques for securing databases against a variety of threats. It also presents schemes of providing access privileges to authorized users. view more..
Ans: The natural join operation operates on two relations and produces a relation as the result. view more..
Ans: Reason to rename a relation is a case where we wish to compare tuples in the same relation. view more..
Ans: SQL permits a variety of functions on character strings. Read to know about them. view more..
Ans: The company is organized into departments. Each department has a unique name, a unique number, and a particular employee who manages the department. We keep track of the start date when that employee began managing the department. A department may have several locations.  A department controls a number of projects, each of which has a unique name, a unique number, and a single location view more..
Ans: Entities and Their Attributes. The basic object that the ER model represents is an entity, which is a thing in the real world with an independent existence. An entity may be an object with a physical existence (for example, a particular person, car, house, or employee) view more..
Ans: A database usually contains groups of entities that are similar. For example, a company employing hundreds of employees may want to store similar information concerning each of the employees. These employee entities share the same attributes, but each entity has its own value(s) for each attribut view more..
Ans: An entity type DEPARTMENT with attributes Name, Number, Locations, Manager, and Manager_start_date. Locations is the only multivalued attribute. We can specify that both Name and Number are (separate) key attributes because each was specified to be unique view more..
Ans: There are several implicit relationships among the various entity types. In fact, whenever an attribute of one entity type refers to another entity type, some relationship exists. For example, the attribute Manager of DEPARTMENT refers to an employee who manages the department; the attribute view more..
Ans: Select clause uses. view more..
Ans: Entity types that do not have key attributes of their own are called weak entity types. In contrast,regular entity types that do have a key attribute—which include all the examples discussed so far—are called strong entity types view more..
Ans: If some cardinality ratio or dependency cannot be determined from the requirements, the users must be questioned further to determine these structural constraints view more..

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