By Anjeev Kr Singh – Computer Science Educator
Published on : May 5, 2021 | Updated on : June 6, 2021
Relational Databases – Notes & Important Points
• A file in a file system is a container to store data in a computer.
• File system suffers from Data Redundancy, Data Inconsistency, Data Isolation, Data Dependence and Controlled Data sharing.
• Database Management System (DBMS) is a software to create and manage databases. A database is a collection of tables.
• Database schema is the design of a database.
• A database constraint is a restriction on the type of data that that can be inserted into the table.
• Database schema and database constraints are stored in database catalog.
• The snapshot of the database at any given time is the database instance.
• A query is a request to a database for information retrieval and data manipulation (insertion, deletion or update). It is written in Structured Query Language (SQL).
• Relational DBMS (RDBMS) is used to store data in related tables. Rows and columns of a table are called tuples and attributed respectively. A table is referred to as a relation.
• Destructions on data stored in a RDBMS is applied by use of keys such as Candidate Key, Primary Key, Composite Primary Key, Foreign Key.
• Primary key in a relation is used for unique identification of tuples.
• Foreign key is used to relate two tables or relations.
• Each column in a table represents a feature (attribute) of a record. Table stores the information for an entity whereas a row represents a record.
• Each row in a table represents a record. A tuple is a collection of attribute values that makes a record unique.
• A tuple is a unique entity whereas attribute values can be duplicate in the table.
• SQL is the standard language for RDBMS systems like MySQL.
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