I will be mostly focusing on SQL databases, along with how to implement a database in AWS cloud.
The information in this blog contains,
- Page 1: What do you mean by database, database languages.
- Page 2: Entity Relation Diagram, Relational schema and converting ER into Relational.
- Page 3: Relational Algebra and Calculus :
- Page 4: Data base design, anomalies present, normalization forms and an example.
Q. What is data and a database?
Data is raw information. For example, your daily usage of mobile. It is raw information about the time you spent on you phone, but if you analyze it, how much time did you spend on an app per day, then it becomes information.
A database is a collection of related data which can be used:
Q. What is Database Management?
A DBMS is a collection of programs which,
- Provide management of databases
- Control access to data present in databases
- Contain a query language to retrieve information easily from a database
An example of database, where data is collected, maintained, and used would be the WordPress site database.
Two main uses of database are,
- Storing information
- Sorting information
Database System = Database + Database Management System
Schema of a database:
Schema describes the logical structure of the database, the overall of the database is also called the database schema.
A schema diagram, as shown below, displays only names of record types (entities) and names of data items (attributes) and does not show the relationships among the various files.
The schema will remain the same while the values filled into it change from instant to instant. When the schema framework is filled in with data item values, it is referred as an instance of the schema.
The data in the database at a particular moment of time is called a database state or snapshot, which is also called the current set of occurrences or instances in the database
1.Data Definition Language(DDL):
- Mainly concerned with definition of data . It is a language that allows the users to define data and their relationship to other types of data.
- It is also used to specify the structure of each table, set of associated values with each attribute, integrity constraints, security and authorization information for each table. The following table gives an overview about usage of DDL statements in SQL
2.Data Manipulation Language(DML):
- Enables user to access or manipulate data
- Insertion of new information into the database
- Deletion of information from the database
- Modification of information stored in the database
3.Data Control Language(DCL):
- DCL statements control access to data and the database using statements such as GRANT and REVOKE.
- The privileges assigned can be SELECT, ALTER, DELETE, EXECUTE, INSERT, INDEX etc. In addition to granting of privileges, you can also revoke (taken back) it by using REVOKE command.
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