Definition: Standard language for managing and manipulating relational databases.

Basic Structure:

SELECT column1, column2 FROM table_name WHERE condition ORDER BY column;

Data Types: INT, VARCHAR, DATE, BOOLEAN, DECIMAL, etc.
Basic Operations:
- DDL (Data Definition Language): Defines database schema.
  - CREATE TABLE table_name (column_name data_type, ...);
  - ALTER TABLE table_name ADD column_name data_type;
  - DROP TABLE table_name;
- DML (Data Manipulation Language): Manages data within tables.
  - INSERT INTO table_name (column1, ...) VALUES (value1, ...);
  - UPDATE table_name SET column1 = value1 WHERE condition;
  - DELETE FROM table_name WHERE condition;
- DCL (Data Control Language): Manages permissions and access.
  - GRANT permission ON object TO user;
  - REVOKE permission ON object FROM user;
- TCL (Transaction Control Language): Manages transactions.
  - COMMIT;
  - ROLLBACK;
  - SAVEPOINT;
Set Operations: UNION, INTERSECT, EXCEPT (or MINUS).
Aggregate Functions: Perform calculations on a set of rows.
- COUNT(), SUM(), AVG(), MIN(), MAX().
- Used with GROUP BY to group rows sharing common values.
- HAVING clause filters groups after aggregation.

Nested Sub-queries: A query embedded within another SQL query.

SELECT * FROM Employees WHERE Salary > (SELECT AVG(Salary) FROM Employees);

Join Expressions: Combining data from multiple tables.
- INNER JOIN: Returns rows when there is a match in both tables.
- LEFT (OUTER) JOIN: Returns all rows from the left table, and matching rows from the right.
- RIGHT (OUTER) JOIN: Returns all rows from the right table, and matching rows from the left.
- FULL (OUTER) JOIN: Returns all rows when there is a match in one of the tables.

Views: Virtual tables based on the result-set of a SQL query.

CREATE VIEW expensive_products AS SELECT * FROM Products WHERE Price > 100;

Transactions: A single logical unit of work performed on a database.
- ACID Properties: Atomicity, Consistency, Isolation, Durability (covered in UNIT-III).
Integrity Constraints: Rules to maintain data accuracy and consistency.
- PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK, DEFAULT.
Authorization: Granting/revoking privileges (e.g., SELECT, INSERT, UPDATE, DELETE) to users.