The Ultimate SQL Cheatsheet

The Ultimate SQL Cheatsheet: Essential Commands, Best Practices & Quick Reference

SQL (Structured Query Language) is the backbone of modern data management. Whether you're just starting out or a seasoned developer, a handy SQL cheatsheet can save you time and prevent common mistakes. This guide offers a quick reference to the most important SQL concepts, commands, and best practices.

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Why Use an SQL Cheatsheet?

• Quick Reference: Instantly recall syntax for common operations.
• Boost Productivity: Write queries faster and with fewer errors.
• Best Practices: Avoid mistakes and follow industry standards.
• SEO Benefit: Improve your database-related content’s visibility.

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🧱 SQL Language Categories DDL (Data Definition Language): Define or alter the structure of database objects like tables. → CREATE, ALTER, DROP

DML (Data Manipulation Language): Add or modify data within tables. → INSERT, UPDATE, DELETE

DQL (Data Query Language): Retrieve data from the database. → SELECT

DCL (Data Control Language): Control access to data and permissions. → GRANT, REVOKE

TCL (Transaction Control Language): Manage transactions and rollbacks. → COMMIT, ROLLBACK, SAVEPOINT

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Common Database Objects

• TABLE: Stores structured data.
• VIEW: A saved query as a virtual table.
• INDEX: Speeds up data retrieval.
• TRIGGER: Executes on specific DB events.

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Essential SQL Commands

DDL (Data Definition Language)

CREATE TABLE Students (
  rollno INT PRIMARY KEY,
  name VARCHAR(30),
  age INT,
  email VARCHAR(100)
);

ALTER TABLE Students ADD email VARCHAR(100);
ALTER TABLE Students MODIFY email VARCHAR(200);
ALTER TABLE Students DROP COLUMN email;
DROP TABLE Students;

DML (Data Manipulation Language)

INSERT INTO Students (rollno, name, age) VALUES (234, 'Donal', 21);
UPDATE Students SET age = 22 WHERE rollno = 234;
DELETE FROM Students WHERE rollno = 234;

DQL (Data Query Language)

SELECT * FROM Students;
SELECT * FROM Students WHERE rollno = 234;
SELECT name, grade FROM Students ORDER BY gender;
SELECT * FROM Students INNER JOIN Section ON Students.section_id = Section.id;

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SQL Joins Explained

• INNER JOIN: Matching rows in both tables.
• LEFT JOIN: All rows from the left, matched from the right.
• RIGHT JOIN: All rows from the right, matched from the left.
• FULL OUTER JOIN: All matching rows from both sides.

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Set Operations

• UNION: Combine and remove duplicates.
• UNION ALL: Combine and keep duplicates.
• INTERSECT: Only common rows.
• EXCEPT/MINUS: Rows in first query not in the second.

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Constraints & Data Integrity

• PRIMARY KEY: Uniquely identifies records.
• FOREIGN KEY: Connects two tables.
• UNIQUE: All values must differ.
• CHECK: Restricts input values.
• DEFAULT: Auto-fills when empty.
• NOT NULL: Value must be present.

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Aggregation Functions

• AVG() – Average value
• MIN() – Minimum value
• MAX() – Maximum value
• SUM() – Total value
• COUNT() – Row count

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SQL Best Practices

• Consistent naming conventions (snake_case / camelCase).
• Readable formatting: Use line breaks and indents.
• *Avoid SELECT : Fetch only what you need.
• Use parameterized queries to avoid SQL injection.
• Normalize your schema: Reduce redundancy.
• Index smartly: Prioritize columns used in filtering and joining.
• Comment and document: Future-proof your work.
• Always test on staging/sample data first.

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Conclusion

A reliable SQL cheatsheet is an essential tool for every developer and analyst. Keep this guide handy to write clean, fast, and secure queries with confidence.