Unit 3: Structured Query Language

SQL:

SQL (Structured Query Language) is a 4th Generation database computer language designed for the retrieval and management of data in relational database management systems (RDBMS), database scheme creation and modification, and database object access control management.

SQL is pronounced as 'sequel' or as S-Q-L.

SQL is a querying language for querying and modifying data and managing databases. SQL was standardized first by the ANSI and later by the ISO. Most database management systems implement a majority of one of these standards and add their proprietary extensions. SQL allows the retrieval, insertion, updating, and deletion of data. A database management system also includes management and administrative functions. Most – if not all – implementations also include a command-line interface (SQL/CLI) that allows for the entry and execution of the language commands, as opposed to only providing an application programming interface (API) intended for access from a graphical user interface (GUI).

Relational Database management:

A relational database organises information through a series of related tables.

and at its simplest is a set of tables used for storing data. Each table has a unique name and may relate to one or more other tables in the database through common values.

Tables
A table in a database is a collection of rows and columns. Tables are also known as entities or relations.

Rows
A row contains data pertaining to a single item or record in a table. Rows are also known as records or tuples.

Columns
A column contains data representing a specific characteristic of the records in the table. Columns are also known as fields or attributes.

Relationships
A relationship is a link between two tables (i.e, relations). Relationships make it possible to find data in one table that pertains to a specific record in another table.

Datatypes
Each of a table's columns has a defined datatype that specifies the type of data that can exist in that column. For example, the FirstName column might be defined as varchar(20), indicating that it can contain a string of up to 20 characters. Unfortunately, datatypes vary widely between databases.

Primary Keys
Most tables have a column or group of columns that can be used to identify records. For example, an Employees table might have a column called EmployeeID that is unique for every row. This makes it easy to keep track of a record over time and to associate a record with records in other tables.

Foreign Keys
Foreign key columns are columns that link to primary key columns in other tables, thereby creating a relationship. For example, the Customers table might have a foreign key column called SalesRep that links to EmployeeID, the primary key in the Employees table.
 

SQL Introduction - Tamil Video:

Introduction to SQL Video:

Structured Query Language (SQL)- Presentation 2:

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