SQL, which stands for Structured Query Language, is a powerful programming language designed for managing and manipulating relational databases.
It is widely used for interacting with databases to perform tasks such as querying data, updating records, inserting new data, and more.
Here are some key concepts and aspects of SQL:
SQL is primarily used with relational database management systems (RDBMS), which organize data into tables with rows and columns. Each table represents a specific entity or relationship, and relationships between tables are defined using keys.
SELECT Command: Retrieves data from one or more tables.
INSERT Command: To Add one or more new records to a table.
UPDATE Command: To Modify one or more existing records in a table.
DELETE Command: Remove one or more records from a table.
CREATE: Creates new database objects, such as tables, indexes, or views.
ALTER: Alter/Modify the structure of an existing database object.
DROP: Deletes a database object.
DDL statements are used for defining the structure of the database, such as creating or modifying tables and indexes.
DML statements are used for manipulating data stored in the database, such as querying, inserting, updating, and deleting records.
DQL is a subset of SQL used for querying and retrieving data from one or more tables. The primary DQL statement is the SELECT statement.
Joins are used to combine rows from two or more tables based on a related column between them. Common types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
Constraints ensure the integrity and accuracy of the data stored in the database. Examples include PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, and CHECK constraints.
Indexes improve the performance of database queries by providing a quick lookup mechanism. They are created on columns to speed up data retrieval operations.
SQL supports transactions, which are sequences of one or more SQL statements that are executed as a single unit. Transactions ensure the consistency and reliability of the database.