SQL Syntax and Structure

1. SQL Statements

SQL statements are the commands used to interact with a database. They can be used to perform various operations such as querying data, inserting new records, updating existing records, and deleting records.

Example:

SELECT * FROM employees; INSERT INTO employees (name, age) VALUES ('John Doe', 30); UPDATE employees SET age = 31 WHERE name = 'John Doe'; DELETE FROM employees WHERE name = 'John Doe';

2. SQL Clauses

SQL clauses are components of SQL statements that perform specific tasks. Common clauses include SELECT, FROM, WHERE, ORDER BY, and GROUP BY.

Example:

SELECT name, age FROM employees WHERE department = 'Sales' ORDER BY age DESC;

3. SQL Operators

SQL operators are used to perform operations on data within SQL statements. Common operators include arithmetic operators (+, -, *, /), comparison operators (=, >, <, !=), and logical operators (AND, OR, NOT).

Example:

SELECT name, salary FROM employees WHERE salary > 50000 AND department = 'Engineering';

4. SQL Data Types

SQL data types define the type of data that can be stored in a database column. Common data types include INT, VARCHAR, DATE, FLOAT, and BOOLEAN.

Example:

CREATE TABLE employees ( id INT PRIMARY KEY, name VARCHAR(100), age INT, salary FLOAT, hire_date DATE );

5. SQL Functions

SQL functions are built-in routines that perform specific tasks. Common functions include aggregate functions (COUNT, SUM, AVG), string functions (CONCAT, LENGTH), and date functions (NOW, DATE_FORMAT).

Example:

SELECT COUNT(*) AS total_employees FROM employees; SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM employees; SELECT DATE_FORMAT(hire_date, '%Y-%m-%d') AS formatted_date FROM employees;