SQL-Simple-Command-Sheet

I am deciding to create this because every time I look up some simple command sheet for SQL I can never manage to find a very simple, dumbed-down version to help me become more efficient at coding. I do not know about everyone else, but for me, I know what all the commands do. however, whenever it comes to remembering them off the top of my head Since I am new I still struggle and would greatly appreciate a place to go to just get a reminder occasionally. So I am going to slowly make a database of all the commands and what they do.

Then maybe later create an example area for each command however I do not know if that will be necessary.

SQL Commands Reference

Command	Description	Example
SELECT	Retrieves data from one or more tables.	SELECT * FROM employees;
INSERT INTO	Adds new rows of data to a table.	INSERT INTO employees (id, name, age) VALUES (1, 'John Doe', 30);
UPDATE	Modifies existing records in a table.	UPDATE employees SET age = 31 WHERE id = 1;
DELETE	Removes records from a table.	DELETE FROM employees WHERE id = 1;
CREATE TABLE	Defines a new table structure.	CREATE TABLE employees (id INT PRIMARY KEY, name VARCHAR(50), age INT);
ALTER TABLE	Modifies an existing table (add, delete, modify columns).	ALTER TABLE employees ADD COLUMN salary DECIMAL(10,2);
DROP TABLE	Deletes a table and all its data.	DROP TABLE employees;
TRUNCATE TABLE	Deletes all rows from a table but keeps its structure.	TRUNCATE TABLE employees;
CREATE DATABASE	Creates a new database.	CREATE DATABASE company;
DROP DATABASE	Deletes an entire database.	DROP DATABASE company;
JOIN	Combines rows from multiple tables based on a related column.	SELECT employees.name, departments.name FROM employees JOIN departments ON employees.dept_id = departments.id;
LEFT JOIN	Returns all records from the left table and matching records from the right table.	SELECT employees.name, departments.name FROM employees LEFT JOIN departments ON employees.dept_id = departments.id;
RIGHT JOIN	Returns all records from the right table and matching records from the left table.	SELECT employees.name, departments.name FROM employees RIGHT JOIN departments ON employees.dept_id = departments.id;
FULL JOIN	Returns all records when there is a match in either table.	SELECT employees.name, departments.name FROM employees FULL JOIN departments ON employees.dept_id = departments.id;
WHERE	Filters records based on a condition.	SELECT * FROM employees WHERE age > 30;
GROUP BY	Groups rows with the same values in specified columns.	SELECT dept_id, COUNT(*) FROM employees GROUP BY dept_id;
HAVING	Filters groups after GROUP BY.	SELECT dept_id, COUNT(*) FROM employees GROUP BY dept_id HAVING COUNT(*) > 5;
ORDER BY	Sorts results in ascending (ASC) or descending (DESC) order.	SELECT * FROM employees ORDER BY age DESC;
LIMIT	Restricts the number of returned records.	SELECT * FROM employees LIMIT 10;
OFFSET	Skips a specified number of rows before returning results.	SELECT * FROM employees LIMIT 10 OFFSET 5;
UNION	Combines result sets from two SELECT queries.	SELECT name FROM employees UNION SELECT name FROM managers;
UNION ALL	Combines result sets and includes duplicates.	SELECT name FROM employees UNION ALL SELECT name FROM managers;
EXISTS	Checks if a subquery returns any results.	SELECT * FROM employees WHERE EXISTS (SELECT 1 FROM departments WHERE dept_id = employees.dept_id);
CASE	Implements conditional logic in queries.	SELECT name, CASE WHEN age > 30 THEN 'Senior' ELSE 'Junior' END AS level FROM employees;
DISTINCT	Returns unique values in a column.	SELECT DISTINCT dept_id FROM employees;
COUNT()	Counts the number of rows that match a condition.	SELECT COUNT(*) FROM employees;
AVG()	Calculates the average value of a numeric column.	SELECT AVG(salary) FROM employees;
SUM()	Calculates the total sum of a numeric column.	SELECT SUM(salary) FROM employees;
MIN()	Retrieves the smallest value in a column.	SELECT MIN(age) FROM employees;
MAX()	Retrieves the largest value in a column.	SELECT MAX(salary) FROM employees;
SUBQUERY	A query nested inside another query.	SELECT name FROM employees WHERE dept_id = (SELECT id FROM departments WHERE name = 'HR');
INDEX	Speeds up searches in a table.	CREATE INDEX idx_name ON employees(name);
VIEW	Creates a virtual table based on a query.	CREATE VIEW employee_salaries AS SELECT name, salary FROM employees;