Mobile databases are separate from the main database and can easily be transported to various places. Even though they are not connected to the main database, they can still communicate with the database to share and exchange data.The mobile database includes the following components −The main system database that stores all the data and is linked to the mobile database.The mobile database that allows users to view information even while on the move. It shares information with the main database.The device that uses the mobile database to access data. This device can be a mobile phone, laptop etc.A communication link ... Read More

There may be times when the SQL query was expecting some data type but it got another. In that case type conversion is done by SQL. This is implicit type conversion. However, sometimes the programmer explicitly converts one data type into another in a query. This is known as explicit type conversion. Both of these in detail are given as follows:Implicit Data Type ConversionIn implicit data type conversion, the SQL programmer does not specify anything. Rather the system converts one type of data to another as per its requirements. For example - a numeric data type can be converted to ... Read More

Mathematical functions are very important in SQL to implement different mathematical concepts in queries.Some of the the major mathematical functions in SQL are as follows −ABS(X)This function returns the absolute value of X. For example −Select abs(-6);This returns 6.MOD(X, Y)The variable X is divided by Y and their remainder is returned. For example −Select mod(9, 5);This returns 4.SIGN(X)This method returns 1 if X is positive, -1 if it is negative and 0 if the value of X is 0. For example −Select sign(10);This returns 1.FLOOR(X)This returns the largest integer value that is either less than X or equal to it. ... Read More

The date and time functions in DBMS are quite useful to manipulate and store values related to date and time.The different date and time functions are as follows −ADDDATE(DATE, DAYS)The numbers of days in integer form (DAYS) is added to the specified date. This is the value returned by the function. For example −sql> SELECT ADDDATE('2018-08-01', 31); +---------------------------------------------------------+ | DATE_ADD('2018-08-01', INTERVAL 31 DAY)                 | +---------------------------------------------------------+ | 2018-09-01                                             | +---------------------------------------------------------+ 1 ... Read More

The select statement is used to get the required data from the database according to the conditions, if any. This data is returned in the form of a table.The basic syntax of the select statement is −Select column 1, column 2 ... column N From table_nameAn example of the select statement is −Student_NumberStudent_NameStudent_PhoneStudent_MarksStudent_MajorSubject1Andrew661592728495Literature2Sara658365486565Maths3Harry464756746348Literature4Sally653783708430Literature5Anne745733773288MathsQuery −Select Student_Name From StudentThis query yields the following result −Student_NameAndrewSaraHarrySallyAnneClauses in Select statementThe example of select statement given above is quite simple and not that useful in practice. So, there are many other clauses associated with select statement that make it more meaningful. Some of these are ... Read More

The different types of keys in DBMS are −Candidate Key - The candidate keys in a table are defined as the set of keys that is minimal and can uniquely identify any data row in the table.Primary Key - The primary key is selected from one of the candidate keys and becomes the identifying key of a table. It can uniquely identify any data row of the table.Super Key - Super Key is the superset of primary key. The super key contains a set of attributes, including the primary key, which can uniquely identify any data row in the table.Composite Key -  If ... Read More

The ANSI-SPARC database architecture is the basis of most of the modern databases.The three levels present in this architecture are Physical level, Conceptual level and External level.The details of these levels are as follows −Physical LevelThis is the lowest level in the three level architecture. It is also known as the internal level. The physical level describes how data is actually stored in the database. In the lowest level, this data is stored in the external hard drives in the form of bits and at a little high level, it can be said that the data is stored in files ... Read More

An Object relational model is a combination of a Object oriented database model and a Relational database model. So, it supports objects, classes, inheritance etc. just like Object Oriented models and has support for data types, tabular structures etc. like Relational data model.One of the major goals of Object relational data model is to close the gap between relational databases and the object oriented practises frequently used in many programming languages such as C++, C#, Java etc.History of Object Relational Data ModelBoth Relational data models and Object oriented data models are very useful. But it was felt that they both ... Read More

Object oriented data model is based upon real world situations. These situations are represented as objects, with different attributes. All these object have multiple relationships between them.Elements of Object oriented data modelObjectsThe real world entities and situations are represented as objects in the Object oriented database model.Attributes and MethodEvery object has certain characteristics. These are represented using Attributes. The behaviour of the objects is represented using Methods.ClassSimilar attributes and methods are grouped together using a class. An object can be called as an instance of the class.InheritanceA new class can be derived from the original class. The derived class contains ... Read More

Database Management System is quite useful compared to the file based management system. However, it does have some disadvantages. Some of those are as follows −More CostlyCreating and managing a database is quite costly. High cost software and hardware is required for the database. Also highly trained staff is required to handle the database and it also needs continuous maintenance. All of these ends up making a database quite a costly venture.High ComplexityA Database Management System is quite complex as it involves creating, modifying and editing a database. Consequently, the people who handle a database or work with it need ... Read More