Structured Query Language

Structured Query Language (SQL)

General Understanding

• SQL is a standardised language for managing and manipulating databases.
• It is designed to handle data in a relational database management system (RDBMS) or for stream processing in a relational data stream management system (RDSMS).
• SQL is both declarative and procedural, allowing you to describe what you want done, and also how it should be done.

Basic Commands

• SELECT is the most common SQL command, used to query the database for specific data.
• INSERT INTO adds new data into a database.
• UPDATE modifies the records in a database.
• DELETE removes records from a database.
• CREATE DATABASE creates a new database.
• ALTER DATABASE modifies the structure of a database.
• CREATE TABLE creates a new table in the database.
• ALTER TABLE modifies the structure of a table.

Advanced Functions

• JOIN is used to combine rows from two or more tables, based on a related column between them.
• Inner JOIN returns records that have matching values in both tables.
• Left (Outer) JOIN returns all records from the left table, and the matched records from the right table.
• Right (Outer) JOIN returns all records from the right table, and the matched records from the left table.
• Full (Outer) JOIN returns all records when there is a match in either the left or the right table.

Implementing SQL in Programming

• SQL commands can be embedded in other programming languages using SQL libraries.
• These libraries provide the methods to connect to the database, execute SQL commands and process the results.

Security and Integrity

• GRANT gives user’s access privileges to a database.
• REVOKE withdraws user’s access privileges to a database previously granted.
• SQL also provide constraints which are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table.