SQL #query #languagelearning #shortsviral #tutorial #databaseconcepts #cheatsheet #luckyxplorer

SQL #query #languagelearning #shortsviral #tutorial #databaseconcept #cheatsheet #luckyxplorer #sql
Essential SQL Commands

1. Data Definition Language (DDL)

These commands define and modify database structures.

CommandDescriptionCREATECreates a new table, view, or database.ALTERModifies an existing table structure.DROPDeletes tables, views, or databases.TRUNCATERemoves all records from a table (faster than DELETE).

Example:

CREATE TABLE employees ( id INT PRIMARY KEY, name VARCHAR(100), position VARCHAR(50) );

2. Data Manipulation Language (DML)

Used for data operations (add, update, delete).

CommandDescriptionINSERTAdds new data into a table.UPDATEModifies existing data.DELETERemoves data from a table.

Example:
INSERT INTO employees (id, name, position) VALUES (1, 'Alice', 'Manager'); UPDATE employees SET position = 'Director' WHERE name = 'Alice'; DELETE FROM employees WHERE id = 1;

3. Data Query Language (DQL)

Used for querying data.

CommandDescriptionSELECTRetrieves data from one or more tables.
SELECT name, position FROM employees WHERE position = 'Manager';

4. Data Control Language (DCL)

CommandDescriptionGRANTGives user access privileges.REVOKERemoves user access privileges.

5. Transaction Control Language (TCL)

CommandDescriptionBEGINBegins a transaction.COMMITSaves changes.ROLLBACKReverts changes.

🔹 SQL Clauses

ClauseUseWHEREFilters rows.ORDER BYSorts results.GROUP BYGroups rows for aggregation.HAVINGFilters groups.LIMIT / TOPLimits result rows.

🔹 SQL Joins

Joins are used to retrieve data from multiple tables based on related columns.

1. INNER JOIN

Returns rows where there is a match in both

SELECT e.name, d.department_name FROM employees e INNER JOIN departments d ON e.department_id = d.id;

2. LEFT JOIN (or LEFT OUTER JOIN)

Returns all rows from the left table, and matched rows from the right table. Fills with NULL if no match

SELECT e.name, d.department_name FROM employees e LEFT JOIN departments d ON e.department_id = d.id;

3. RIGHT JOIN (or RIGHT OUTER JOIN)

Returns all rows from the right table, and matched rows from the left.
SELECT e.name, d.department_name FROM employees e RIGHT JOIN departments d ON e.department_id = d.id;

4. FULL OUTER JOIN

Returns rows when there is a match in one of the tables. Not supported in some databases like MySQL without using UNION.
SELECT e.name, d.department_name FROM employees e FULL OUTER JOIN departments d ON e.department_id = d.id;

5. CROSS JOIN

Returns the Cartesian product of both tables.

sql
SELECT e.name, d.department_name FROM employees e CROSS JOIN departments d;

6. SELF JOIN

Joins a table with itself.

sql

SELECT a.name AS employee, b.name AS manager FROM employees a JOIN employees b ON a.manager_id = b.id;

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