Programming40 entries
SQL Reference
SELECT, JOIN, GROUP BY, subqueries, indexes, and database manipulation commands
1Querying Data
SELECT * FROM table | Select all columns from table |
SELECT col1, col2 FROM table | Select specific columns |
SELECT DISTINCT col FROM table | Select unique values only |
SELECT col AS alias FROM table | Column alias |
SELECT COUNT(*) FROM table | Count total rows |
SELECT * FROM table LIMIT 10 | Limit results to 10 rows |
SELECT * FROM table LIMIT 10 OFFSET 20 | Pagination (skip 20, take 10) |
2Filtering & Sorting
WHERE col = value | Filter by exact match |
WHERE col != value / WHERE col <> value | Not equal |
WHERE col > 10 AND col < 100 | Range with AND |
WHERE col IN (1, 2, 3) | Match any value in list |
WHERE col NOT IN (1, 2, 3) | Exclude values in list |
WHERE col BETWEEN 10 AND 100 | Range inclusive |
WHERE col LIKE "%pattern%" | Pattern match (% = any chars) |
WHERE col IS NULL / IS NOT NULL | Check for NULL values |
ORDER BY col ASC|DESC | Sort results |
ORDER BY col1 ASC, col2 DESC | Multi-column sort |
3Joins
INNER JOIN t2 ON t1.id = t2.fk | Only matching rows from both tables |
LEFT JOIN t2 ON t1.id = t2.fk | All from left + matching from right |
RIGHT JOIN t2 ON t1.id = t2.fk | All from right + matching from left |
FULL OUTER JOIN t2 ON t1.id = t2.fk | All rows from both tables |
CROSS JOIN t2 | Cartesian product (all combinations) |
self JOIN: FROM t1 a JOIN t1 b | Join table with itself |
4Aggregation
COUNT(col) / COUNT(*) | Count non-null values / all rows |
SUM(col) | Sum of values |
AVG(col) | Average of values |
MIN(col) / MAX(col) | Minimum / maximum value |
GROUP BY col | Group rows by column |
HAVING COUNT(*) > 5 | Filter groups (like WHERE for groups) |
5Data Modification
INSERT INTO t (col) VALUES (val) | Insert single row |
INSERT INTO t (col) VALUES (v1), (v2) | Insert multiple rows |
UPDATE t SET col = val WHERE id = 1 | Update specific rows |
DELETE FROM t WHERE id = 1 | Delete specific rows |
TRUNCATE TABLE t | Remove all rows (fast, no logging) |
6Table Operations
CREATE TABLE t (id INT PRIMARY KEY, ...) | Create table |
ALTER TABLE t ADD col TYPE | Add column |
ALTER TABLE t DROP COLUMN col | Remove column |
ALTER TABLE t RENAME TO new_name | Rename table |
DROP TABLE t | Delete table |
CREATE INDEX idx ON t(col) | Create index |
Related Cheatsheets
JavaScript ES6+
Modern JavaScript syntax: destructuring, arrow functions, promises, modules, and built-in methods
Python Essentials
Python syntax, data structures, comprehensions, built-in functions, and common patterns
Regular Expressions
Regex syntax, character classes, quantifiers, groups, lookaheads, and common patterns