Create RDBMS.md

About Relation Database Management system (SQL)

blogs/RDBMS.md

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+<h1> What is Relational Model? </h1>
+
+**Relational Model (RM)** represents the database as a collection of relations. A relation is nothing but a table of values. Every row in the table represents a collection of related data 
+values. These rows in the table denote a real-world entity or relationship. The table name and column names are helpful to interpret the meaning of values in each row. 
+The data are represented as a set of relations. In the relational model, data are stored as tables. However, the physical storage of the data is independent of the way the data are logically 
+organized. 
+
+<h1>Relational Model Concepts</h1>
+
+1. Attribute: Each column in a Table. Attributes are the properties which define a relation. e.g., Student_Rollno, NAME,etc. 
+2. Tables – In the Relational model the, relations are saved in the table format. It is stored along with its entities. A table has two properties rows and columns. Rows represent records and columns represent attributes. 
+3. Tuple – It is nothing but a single row of a table, which contains a single record. 
+4. Relation Schema: A relation schema represents the name of the relation with its attributes. 
+5. Degree: The total number of attributes which in the relation is called the degree of the relation. 
+6. Cardinality: Total number of rows present in the Table. 
+7. Column: The column represents the set of values for a specific attribute. 
+8. Relation instance – Relation instance is a finite set of tuples in the RDBMS system. Relation instances never have duplicate tuples. 
+9. Relation key - Every row has one, two or multiple attributes, which is called relation key. 
+10. Attribute domain – Every attribute has some pre-defined value and scope which is known as attribute domain Keys in DBMS 
+
+<h1>KEYS</h1>
+
+**KEYS in DBMS** is an attribute or set of attributes which helps you to identify a row(tuple) in a relation(table). They allow you to find the relation between two tables. Keys help you 
+uniquely identify a row in a table by a combination of one or more columns in that table. Key 
+is also helpful for finding unique record or row from the table. Database key is also helpful for finding unique record or row from the table. 
+
+<h1>Why we need a Key?</h1>
+Here are some reasons for using sql key in the DBMS system.
+
+- Keys help you to identify any row of data in a table. In a real-world application, a 
+table could contain thousands of records. Moreover, the records could be 
+duplicated. 
+Keys ensure that you can uniquely identify a table record despite these challenges. 
+- Allows you to establish a relationship between and identify the relation between 
+tables 
+- Help you to enforce identity and integrity in the relationship. 
+Types of Keys in Database Management System 
+There are mainly seven different types of Keys in DBMS and each key has its different 
+functionality: 
+- Super Key - A super key is a group of single or multiple keys which identifies 
+rows in a table. 
+- Primary Key - is a column or group of columns in a table that uniquely identify 
+every row in that table. 
+DATABASE MANAGEMENT SYSTEMS Page 30
+- Candidate Key - is a set of attributes that uniquely identify tuples in a table. 
+Candidate Key is a super key with no repeated attributes. 
+- Alternate Key - is a column or group of columns in a table that uniquely identify 
+every row in that table. 
+- Foreign Key - is a column that creates a relationship between two tables. The 
+purpose of Foreign keys is to maintain data integrity and allow navigation 
+between two different instances of an entity. 
+- Compound Key - has two or more attributes that allow you to uniquely 
+recognize a specific record. It is possible that each column may not be unique by 
+itself within the database. 
+- Composite Key - An artificial key which aims to uniquely identify each record is 
+called a surrogate key. These kind of key are unique because they are created 
+when you don't have any natural primary key. 
+- Surrogate Key - An artificial key which aims to uniquely identify each record is 
+called a surrogate key. These kind of key are unique because they are created 
+when you don't have any natural primary key. 
+
+
+**Primary key example:** 
+
+``CREATE TABLE Persons ( 
+ ID int NOT NULL, 
+ LastName varchar(255) NOT NULL, 
+ FirstName varchar(255), 
+ Age int, 
+ PRIMARY KEY (ID) 
+);``
+
+<h1>ER model</h1> 
+
+- ER model stands for an Entity-Relationship model. It is a high-level data model. This model is used to define the data elements and relationship for a specified system. 
+- It develops a conceptual design for the database. It also develops a very simple and easy to design view of data.
+- In ER modeling, the database structure is portrayed as a diagram called an entityrelationship diagram. 
+
+``For example``, Suppose we design a school database. In this database, the student will be an 
+entity with attributes like address, name, id, age, etc. The address can be another entity with 
+attributes like city, street name, pin code, etc and there will be a relationship between them. 
+
+
+<h1>Relational Algebra</h1>
+
+- Relational Algebra is procedural query language, which takes Relation as input and generates relation as output. Relational algebra mainly provides theoretical 
+foundation for relational databases and SQL. 
+- Relational algebra is a procedural query language, it means that it tells what data to be retrieved and how to be retrieved. 
+- Relational Algebra works on the whole table at once, so we do not have to use loops etc to iterate over all the rows (tuples) of data one by one. 
+- All we have to do is specify the table name from which we need the data, and in a single line of command, relational algebra will traverse the entire given table to 
+fetch data for you. 
+
+
+<h2>Basic/Fundamental Operations: </h2>
+
+1.Select (σ) 
+2. Project (∏) 
+3. Union ( ) 
+4. Set Difference (-) 
+5. Cartesian product (X) 
+6. Rename (ρ) 
+
+ <h2>Select Operation (σ) :</h2>
+
+This is used to fetch rows (tuples) from table(relation) which satisfies a given condition. Syntax: σp(r)
+
+➢ σ is the predicate
+
+➢ r stands for relation which is the name of the table 
+
+➢ p is prepositional logic ex: σage > 17 (Student)
+
+<h2>Project Operation (∏): </h2>
+
+- Project operation is used to project only a certain set of attributes of a relation. In simple words, If you want to see only the names all of the students in the Student table, then 
+you can use Project Operation. 
+- It will only project or show the columns or attributes asked for, and will also remove duplicate data from the columns. 
+
+
+<h2>Union Operation (U): </h2>
+
+- This operation is used to fetch data from two relations(tables) or temporary relation(result of another operation). 
+- For this operation to work, the relations(tables) specified should have same number of attributes(columns) and same attribute domain. Also the duplicate tuples are 
+autamatically eliminated from the result. 
+
+<h2>Set Difference (-):</h2>
+
+This operation is used to find data present in one relation and not present in the 
+second relation. This operation is also applicable on two relations, just like Union 
+operation. 
+
+<h2>Rename Operation (ρ):</h2>
+
+This operation is used to rename the output relation for any query operation which returns 
+result like Select, Project etc. Or to simply rename a relation(table)
+
+<h1>Join in DBMS:</h1>
+
+- A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
+- Join in DBMS is a binary operation which allows you to combine join product and selection in one single statement. 
+- The goal of creating a join condition is that it helps you to combine the data from two or more DBMS tables. 
+- The tables in DBMS are associated using the primary key and foreign keys.
+
+
+Types of SQL JOIN
+
+``1. INNER JOIN`` 
+In SQL, INNER JOIN selects records that have matching values in both tables as long as the 
+condition is satisfied. 
+It returns the combination of all rows from both the tables where the condition satisfies. 
+
+``2. LEFT JOIN ``
+The SQL left join returns all the values from left table and the matching values from the right 
+table. If there is no matching join value, it will return NULL. 
+
+``3. RIGHT JOIN`` 
+In SQL, RIGHT JOIN returns all the values from the values from the rows of right table and 
+the matched values from the left table. If there is no matching in both tables, it will return NULL. 
+
+``4. FULL JOIN`` 
+In SQL, FULL JOIN is the result of a combination of both left and right outer join. Join 
+tables have all the records from both tables. It puts NULL on the place of matches not found.