SQL
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SQL stands for Structured Query language, pronounced as "S-Q-L" or sometimes as "See-Quel." SQL is...
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.
Some popular Relational Database management systems are:
In this tutorial, you will learn
Relational Integrity constraints in DBMS are referred to conditions which must be present for a valid relation. These Relational constraints in DBMS are derived from the rules in the mini-world that the database represents.
There are many types of Integrity Constraints in DBMS. Constraints on the Relational database management system is mostly divided into three main categories are:
Domain constraints can be violated if an attribute value is not appearing in the corresponding domain or it is not of the appropriate data type.
Domain constraints specify that within each tuple, and the value of each attribute must be unique. This is specified as data types which include standard data types integers, real numbers, characters, Booleans, variable length strings, etc.
Example:
Create DOMAIN CustomerName CHECK (value not NULL)
The example shown demonstrates creating a domain constraint such that CustomerName is not NULL
An attribute that can uniquely identify a tuple in a relation is called the key of the table. The value of the attribute for different tuples in the relation has to be unique.
Example:
In the given table, CustomerID is a key attribute of Customer Table. It is most likely to have a single key for one customer, CustomerID =1 is only for the CustomerName =" Google".
CustomerID | CustomerName | Status |
1 | Active | |
2 | Amazon | Active |
3 | Apple | Inactive |
Referential Integrity constraints in DBMS are based on the concept of Foreign Keys. A foreign key is an important attribute of a relation which should be referred to in other relationships. Referential integrity constraint state happens where relation refers to a key attribute of a different or same relation. However, that key element must exist in the table.
Example:
In the above example, we have 2 relations, Customer and Billing.
Tuple for CustomerID =1 is referenced twice in the relation Billing. So we know CustomerName=Google has billing amount $300
Four basic update operations performed on relational database model are
Insert, update, delete and select.
Whenever one of these operations are applied, integrity constraints specified on the relational database schema must never be violated.
The insert operation gives values of the attribute for a new tuple which should be inserted into a relation.
You can see that in the below-given relation table CustomerName= 'Apple' is updated from Inactive to Active.
To specify deletion, a condition on the attributes of the relation selects the tuple to be deleted.
In the above-given example, CustomerName= "Apple" is deleted from the table.
The Delete operation could violate referential integrity if the tuple which is deleted is referenced by foreign keys from other tuples in the same database.
In the above-given example, CustomerName="Amazon" is selected
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