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Query,Basic Sub-Query,Complex Sub-Query Query A database query is the use of a select statement to display desired information based on conditions from one or more tables. Different tables in the database store different information. By using query user can view his desired information as desired. For example, let's say that the employees database contains information about many employees. It can display the results of any employee who has joined in the last one year. Use of Select statement: A command of data query language is select statement. A database query is created using SQL statements. A select statement can be used to display data from multiple columns from one or more tables. But remember that select is not an independent statement. It must be accompanied by one or more other clauses for it to work. Some clauses must be used with this, while some clauses are optional. The most commonly used statement in SQL queries is the select statement. Form clause must be used with t...

 View A view is a virtual table. A view looks like a table and works like a table. Apparently it will seem so to the user. In fact, a view is a table built with predefined queries. Some rows or all rows can be shown conditionally between views. Views can be created with one or more tables. When creating a view, the SELECT statement is actually executed, with which the view is created. The SELECT statement used to create the view can use only column names or more complex functions or calculated fields. A view is a predefined query stored in the database, which looks like a table and is used like a table, but which does not occupy any space in the database. A view is created in a database using the create view statement. A new view can be created from data from a single table, multiple tables or any other view. That user must have the necessary privileges to create the view. The syntax of the create view statement is as follows: CREATE [OR REPLACE] [ALGORITHM = (UNDEFINED | MERGE | T...

 Hybrid network A mixed or hybrid network is essentially a combination of client-server and peer-to-peer networks. Generally, the client-server portion dominates in a hybrid network. However, in addition, there are sparsely coupled peer-to-peer network segments. Advantages of a hybrid network are: (i) Client-server applications can be housed and managed centrally. (ii) Users can control access to their respective computer resources and share their resources. Disadvantages of hybrid network are- (i) Having two types of networks makes it difficult for users to access the network. (ii) Need to remember different passwords for workgroups and servers/domains. (iii) Resources are located on different computers and cannot be managed centrally. Different versions of the same file can be scattered across different computers. (iv) Difficulty backing up files stored on different workstations. Network architecture Designing and implementing an effective network with respect to communication ru...

Differences between database indexing and sorting Indexing (i) It takes relatively less time to sort random data. (ii) After indexing the data file in this method, new records are automatically added to the correct location. (iii) Sorting of data file by indexing method keeps serialization of records of file in main table. (iv) When a data file is indexed, a new index file is created and the original table file remains unchanged. (v) Sorting by indexing requires additional space in memory as additional index files are created. (vi) Alphabetically, Numerically, Indexing can be done. Sorting (i) Sorting random data takes more time than indexing.   (ii) After sorting the data file in this method, if new records are added, the file has to be sorted again. (iii) When the data file is sorted by the sorting method, the serialization of the records in the original table file is not correct. (iv) When the data file is sorted, the original table file is stored in memory in a sorted state. (v...

Question-1. What is data type? Answer: In our daily life we ​​have to work with a lot of data. That is why the use of database for personal and institutional needs is increasing day by day. And the database means a collection of many different types of data. Different types of data are divided into categories according to application or use. These different types of data are called data types. When creating a database in Microsoft Access, it is necessary to determine what type of data will be stored in which field. Database programs perform different operations based on the type of data. Any data entry cannot be done in any field. For example - text for data like letters or letters, numbers for data like numbers or numbers etc. Question-2. What are field properties? Or, what are field properties? Answer: Database has some properties for each field of data table. Field properties are displayed depending on the data type. These data properties determine the shape of the field, how the da...

In relational database management systems The features of relational database management system are as follows: (i) Entry can be made easily by creating tables. (ii) Relationships can be created between a data table and one or more other data tables. (iii) Requirement of data can be found out of large amount of data.  (iv) Data entry can be controlled with the help of data validation. (v) Easily exchange information from one database to another. (vi) Fine arithmetic operations can be performed on numerical data. (vii) Reports can be easily generated and printed in various formats. (viii) Labels can be made and printed with required information. (ix) Entry form can be generated. (x) Different types of charts can be created. (ii) Executable (exe) file can be created by converting the program into binary code. (xii) Menus can be easily created with the help of Menu Builder. (xiii) Attractive data entry forms can be created. (xiv) Import or use data from other database programs (eg Fox...

Various components of the database window  A database is in the form of a container or window, in which similar objects in the database are grouped together. The database window consists of several tabs. Database tables and other objects are stored under different tabs, the object to be created is selected from the database window. Below is a brief introduction to the various components of the database window. Tables: The tables are stored under this tab. From here a table can be changed, modified, or a new database created. Queries: From this tab you can get the list of all the queries in the current database. From here one can manage a query, change the query, modify it or create a new query. Forms: All reports and forms of the current database can be found from this tab. From here a report can be modified or a new report can be created. Report: Report is to display or print the information in the format as desired by the users. Page: Database Access page can be created to work w...

Question-1. What is database? Answer: The word Data means data and the word Base means assembly. So a collection of interrelated data that can be stored in a computer is called a database. For example, information of students of an institution, voter list, information of employees of a company, etc. Question-2. What is the field? Answer: Different parts of the record are called fields. Basically column heading is called field. such as  Name, Roll, Class, Age are each separate fields. Question-3. What is the record? Answer: The collection of data of several fields of a Data Table is called Record. Basically, the Record is obtained by combining the data of the rows of the Table. Question-4. What does the word query mean? Answer: Displaying specific data from a database through specific conditions very quickly and easily is called a query. Data can be conveniently selected using expressions, operators, filters, etc. in the query. Queries can be of various types are--- (i) Select Query...

  Data Encryption & Decryption  Data Encryption: Data encryption is to keep data safe from the use of unauthorized persons/organizations. Encrypted data usually prevents unauthorized persons/institutions from accessing the data. The source or sender of the data encrypts the data using specific codes. When the data reaches the destination or recipient, the data has to be decrypted before use. In this case, the sender has to inform the Encrypt rule or the Decrypt rule to the recipient. The original message is changed by decrypting the encrypted data using the same method or algorithm. Different methods of data encryption: There are various types of data encryption rules in use, viz (i) Caesar Code and (ii) Data encryption standards. The Caesar code has been used to encrypt data since the time of Roman Emperor Julius Caesar. The Data Encryption Standard-DES invented by the American National Bureau of Standard NBS is the most widely used encryption method. The method of encryp...

 Basic Concept on Data Security & Authentication Entity Level Security The security system is greatly strengthened by database authorization. Even then, security breaches do occur. Various unauthorized persons breach security through database misuse and accidents. But this is not desirable at all in case of database. Therefore, a security method called encryption is used in the database management system to further strengthen the security system. Data Recovery Database data is lost when the computer system fails or crashes due to any reason. The process by which this lost data can be recovered is called data recovery. Failures are of various types, namely-  (i) Transaction Failure (ii) Logical Error (iii) System Error  (iv) System Crash (v) Disk Failure Authorization Authorization is a process by which database security can be controlled. A database user can have different types of authorizations. This is dependent on database security. When the query processor transl...

Fundamental Operation of SQL SQL in data definition Data is defined or defined using SQL through the CREATE statement. An example is given below CREATE TABLE Employee() Emp_No NUMBER (5) NOT NULL Name CHAR (20) Skill CHAR (20) pay_rate NUMBER (10, 2); Explanation of the statement: (i) A table named Employee can be created through this SQL. The table will have four fields named Emp_No, Name, Skill and Pay_rate. (ii) Emp_No field will be NUMBER type data and this field will never be empty as it is declared as NOT NULL. (iii) Name field will be Character tight data and its length will be 20. (iv) The Skill field will be Character tight data and its length will be 20. (v) Pay_rate field will be NUMBER data type and its length will be 10 and 2 digits after decimal. Now let's say we want to add a new field to this table. Then type the following command: ALTER TABLE Employee ADD Phone_No NUMBER (10); Now type the following command to delete the Employee table. DROP TABLE Employee. SQL in ...

Query Language User can easily retrieve information or data from database with query language. Operations such as entering data, retrieving data, modifying or deleting data in the database are called queries. The language with which queries are made is called query language. Most database management systems use query languages ​​to access the database. It is a high-level language. Using this language, it is possible to easily search and collect data from the database and perform various calculations according to the user's wishes. This language is higher level than any standard programming language. SQL and QUEL query languages ​​are currently used in microcomputers. Name some query languages (i) QUEL (Query Language) (ii) QBE [Query by Example] (iii) SQL (Structured Query Language) (iv) Server SQL Among these four query languages, SQL has gained the most popularity worldwide. According to ANSI standards, SQL has become the standard query language for relational databases. SQL and ...

OBJECT ORIENTED DATABASE MODEL  Object Oriented Database Model: Object-oriented programming is basically divided into two phases: object-oriented analysis and object-oriented design. In the analysis phase, according to the type of problem described in the system, the main problem is divided into several small units or objects, and connections are established based on the results obtained from them. And in the design phase, by reviewing the classes or objects declared in the analysis phase, the classes, member functions and driver programs are designed by determining the class dependency, class hierarchical. Steps of Object Oriented Analysis: (i) Analyzing and understanding the main problem. (ii) Describing user needs. (iii) Dividing the original problem into smaller parts or objects as required. (iv) Determining the properties of objects. (v) Determining the desired results from the objects. (vi) Making connections between objects based on desired and achieved results. Steps of Ob...

Use of Retrieval Update Function from Relational Data Retrieving function description from relational data-- SELECT statement is used for SQL language retrieval. It can also be used to select data from multiple relations. SELECT statement syntax-- SELECT [distinct] <target-list> form <relation__ list> [where <predicate>] Distinct: Specifies that all attributes will be displayed by default. Distinct clause should be used to avoid displaying any duplicate records in the query. Target-list: List all the attributes to be displayed from a table. Multiple attribute names are separated by commas. Relation list: All the tables that will be evaluated i.e. all the tables from which the data will be selected must be mentioned in the <Relation list> part with the form clause. Predicate : Predicate is to be specified with where clause. Here data can be relative from multiple tables by defining a relation attribute as Predicate.

Composition of Network Data Model and Relational Data Model --- Network Data Model A network database contains links between records. This is very similar to the NTT relationship model. Difference between network data model and relational data model: Network Data Model: (i) Linking between records in the database. (ii) Complex linkage between organization records is used. (iii) It is very similar to NTT relationship model. (iv) A record can be connected quickly with the help of organization Relational Data Model: (i) Different types of relationships exist in such databases. (ii) Creates relationships between tables. Records are used. (iii) Many tables are related to each other. (iv) Relationships between one table and another can be linked.

Relational Database If you need to work with data from multiple database files, links can be established between the files. Establishing links to work with data from different table database files is called relational database. There are three types of relational databases, namely -- (i) One to One Relationship (ii) One to many relation (iii) Many to Many relation.   Relational Data Model: In a relational database, logical relationships exist between different types of tables. Different tables are created according to the nature of the data. The records are then used by creating relationships between the tables. That is, many tables are related to each other and one table is related to another table.

Binary Relationship  A data structure diagram that links only two record types is called a binary relationship. This is similar to the binary relationship of the E-R diagram. Binary relationships are basically of 3 types, viz-- (i) One to One (ii) One to Many and (iii) Many to many. If the binary relationship is One to One then the arrow keys will be on either side of the link. But if the relationship is One to Many or Many to One, then either side of the link will have its mark on one side.   General Relationship: Basically, the relationship method that establishes the relationship between more than two records is called general relationship. General relationships are usually shown by boxes and links. For example, consider an E-R diagram made up of three entities, Customer, Account and Branch, which are related to the general relationship CAB.  E-R diagram to show general relationships of network data model Data Structure Diagram following steps should be taken: (i) Enti...

Data Structure Diagram A data structure diagram is a schema that represents the design of a network database. There are two basic components in this diagram. For example, boxes and boxes represent or correspond to record types. Data Structure Diagram is used for the same purpose as Entity Relationship Diagram. That is to say, the data structure diagram specifies the overall logical structure of the database. So, E-R diagram can be translated into Corresponding Data Structure Diagram.

Three types of relationships can be established in a database file, namely— ii) One to One relation ii) One to Many relation (ii) Many to Many relation. These are discussed below-- (i) One to One Relationship: When relationship is established between two database files and one record in one database will have only one record in the other database. That is, if a record in the STAR database is related to only one record in the PRO database, then it is called a One to One relationship. (ii) One to Many relation: This is a widely used relation. In this method, a record in a database is related to multiple records in another database. That is, there may be multiple matches in the PRO database for a record in the STAR database. Think, different suppliers provide different products in an office. In this case there is a database for Supplier and another database is created for Product. Unlike one Supplier item number in the Supplier database, the Product database can have multiple items. In th...

Entity Relationship Diagram It is also possible to show the logical structure or relationships of a database using a block diagram, called an entity relationship diagram. It is much easier to understand the whole thing with the help of block diagram than to describe it in writing. There are some general rules to follow for expressing the database using block diagrams. Apart from that some symbols can be used. The symbols used carry special meanings. Examples of Basic Symbols Used in NTT Relationship Diagrams--- Several symbols can be used to show the logical structure or relationships of a database using block diagrams as well. The symbols used carry special meanings. Some of the common symbols used in the NTT relationship model are--- Rectangle -- Set entity Ellipse- attribute Diamond -- Relationships Straight line -- contains attributes and connectors of NTT sets and NTT sets.