DBMS

Aggregate Functions in SQL

Aggregate functions in SQL evaluates the set of tuple values and returns a relation with a single attribute carrying single tuple value as a result. SQL has five aggregate functions count, average, maximum, minimum, sum. Among these aggregate functions, only ‘sum’ and ‘average’ function operate only on numeric values only while count, maximum, minimum can …

Aggregate Functions in SQL Read More »

Set Operations in SQL

Set operations integrate the outcome of two entirely independent SQL queries. There are three set operations in SQL Union, Intersect, Except. These set operations are based on the principles of mathematical set theory. The set operations are applicable to the type compatible relations only, that means relations involved in operation must have an ‘equal number …

Set Operations in SQL Read More »

Integrity Constraints in DBMS

­Integrity constraints ensure that when the authorized users modify the database they do not disturb the data consistency. Integrity constraints are introduced while designing the database schema. The constraints are specified within the SQL DDL command like ‘create table’ and ‘alter table’ command. Let’s see, the general form of ‘create table’ and ‘alter table’ command …

Integrity Constraints in DBMS Read More »

Null Value in SQL

Null Value in SQL is the special value, allocated to an attribute in a relation which indicates that the information regarding the corresponding attribute is either unknown or it doesn’t even exist. In this section, we will discuss the null values in detail. What is the Null Value in SQL? The null value assigned to …

Null Value in SQL Read More »

Relational Data Model

The relational data model provides conceptual tools to design the database schema of the relational database. The relational model describes the data, relationship between that data, data sematic and constraints on the data in the relational database. The relational model expresses the data and relationship among the data in the form of tables. There is …

Relational Data Model Read More »

Database Languages

Database Languages are the set of statements, that are used to define and manipulate a database. A Database language has Data Definition Language (DDL), which is used to construct a database & it has Data Manipulation Language (DML), which is used to access a database. DDL implements database schema at the physical, logical and external …

Database Languages Read More »

View of Data in DBMS

View of data in DBMS narrate how the data is visualized at each level of data abstraction? Data abstraction allow developers to keep complex data structures away from the users. The developers achieve this by hiding the complex data structures through levels of abstraction. There is one more feature that should be kept in mind …

View of Data in DBMS Read More »

Entity Set

Entity Set is a collection or a group of ‘entities’ sharing exactly the ‘same set of attributes’. All entities can be distinctly identified in an entity set. This is because all the entities have a different set of value for some set of attributes. We further classify the entity set into two basic categories Strong …

Entity Set Read More »