E.F Codd was a Computer Scientist who invented Relational model for Database management. Based on relational model, Relation database was created. Codd proposed 13 rules popularly known as Codd’s 12 rules to test DBMS’s concept against his relational model. Codd’s rule actualy define what quality a DBMS requires in order to become a Relational Database …
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A Relational Database management System(RDBMS) is a database management system based on relational model introduced by E.F Codd. In relational model, data is represented in terms of tuples(rows). RDBMS is used to manage Relational database. Relational database is a collection of organized set of tables from which data can be accessed easily. Relational Database is …
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Database Keys Keys are very important part of Relational database. They are used to establish and identify relation between tables. They also ensure that each record within a table can be uniquely identified by combination of one or more fields within a table. Super Key Super Key is defined as a set of attributes within …
Normalization of Database Database Normalisation is a technique of organizing the data in the database. Normalization is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like Insertion, Update and Deletion Anamolies. It is a multi-step process that puts data into tabular form by removing duplicated data from the relation tables. …
ER-Diagram is a visual representation of data that describes how data is related to each other. Symbols and Notations Components of E-R Diagram The E-R diagram has three main components. 1) Entity An Entity can be any object, place, person or class. In E-R Diagram, an entity is represented using rectangles. Consider an example of …
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Introduction to SQL Structure Query Language(SQL) is a programming language used for storing and managing data in RDBMS. SQL was the first commercial language introduced for E.F Codd’s Relational model. Today almost all RDBMS(MySql, Oracle, Infomix, Sybase, MS Access) uses SQL as the standard database language. SQL is used to perform all type of data …
create command create is a DDL command used to create a table or a database. Creating a Database To create a database in RDBMS, create command is uses. Following is the Syntax, create database database-name; Example for Creating Database create database Test; The above command will create a database named Test. Creating a Table create …
alter command alter command is used for alteration of table structures. There are various uses of alter command, such as, to add a column to existing table to rename any existing column to change datatype of any column or to modify its size. alter is also used to drop a column. To Add Column to …
SQL queries to Truncate, Drop or Rename a Table truncate command truncate command removes all records from a table. But this command will not destroy the table’s structure. When we apply truncate command on a table its Primary key is initialized. Following is its Syntax, truncate table table-name Here is an Example explaining it. truncate …
DML command Data Manipulation Language (DML) statements are used for managing data in database. DML commands are not auto-committed. It means changes made by DML command are not permanent to database, it can be rolled back. 1) INSERT command Insert command is used to insert data into a table. Following is its general syntax, INSERT …
TCL command Transaction Control Language(TCL) commands are used to manage transactions in database.These are used to manage the changes made by DML statements. It also allows statements to be grouped together into logical transactions. Commit command Commit command is used to permanently save any transaaction into database. Following is Commit command’s syntax, commit; Rollback command …
Data Control Language(DCL) is used to control privilege in Database. To perform any operation in the database, such as for creating tables, sequences or views we need privileges. Privileges are of two types, System : creating session, table etc are all types of system privilege. Object : any command or query to work on tables …
Where clause is used to specify condition while retriving data from table. Where clause is used mostly withSelect, Update and Delete query. If condititon specified by where clause is true then only the result from table is returned. Syntax for WHERE clause SELECT column-name1, column-name2, column-name3, column-nameN from table-name WHERE [condition]; Example using WHERE clause …
Select query is used to retrieve data from a tables. It is the most used SQL query. We can retrieve complete tables, or partial by mentioning conditions using WHERE clause. Syntax of SELECT Query SELECT column-name1, column-name2, column-name3, column-nameN from table-name; Example for SELECT Query Conside the following Student table, S_id S_Name age address 101 …
Like clause is used as condition in SQL query. Like clause compares data with an expression using wildcard operators. It is used to find similar data from the table. Wildcard operators There are two wildcard operators that are used in like clause. Percent sign % : represents zero, one or more than one character. Underscore …
Order by clause is used with Select statement for arranging retrieved data in sorted order. The Order byclause by default sort data in ascending order. To sort data in descending order DESC keyword is used withOrder by clause. Syntax of Order By SELECT column-list|* from table-name order by asc|desc; Example using Order by Consider the …
Group by clause is used to group the results of a SELECT query based on one or more columns. It is also used with SQL functions to group the result from one or more tables. Syntax for using Group by in a statement. SELECT column_name, function(column_name) FROM table_name WHERE condition GROUP BY column_name Example of …
having clause is used with SQL Queries to give more precise condition for a statement. It is used to mention condition in Group based SQL functions, just like WHERE clause. Syntax for having will be, select column_name, function(column_name) FROM table_name WHERE column_name condition GROUP BY column_name HAVING function(column_name) condition Example of HAVING Statement Consider the …
The distinct keyword is used with Select statement to retrieve unique values from the table. Distinctremoves all the duplicate records while retrieving from database. Syntax for DISTINCT Keyword SELECT distinct column-name from table-name; Example Consider the following Emp table. eid name age salary 401 Anu 22 5000 402 Shane 29 8000 403 Rohan 34 10000 …
AND and OR operators are used with Where clause to make more precise conditions for fetching data from database by combining more than one condition together. AND operator AND operator is used to set multiple conditions with Where clause. Example of AND Consider the following Emp table eid name age salary 401 Anu 22 5000 …