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Cheatsheet
SQL
Essential commands for querying and managing data.
Querying
| SELECT * FROM t | Retrieve all columns |
| SELECT col AS alias FROM t | Column alias |
| SELECT DISTINCT col FROM t | Remove duplicates |
| SELECT TOP 10 * FROM t | Limit rows (SQL Server) |
| SELECT * FROM t LIMIT 10 | Limit rows (MySQL/PostgreSQL) |
Filtering & Sorting
| WHERE col = 'value' | Exact match |
| WHERE col LIKE 'A%' | Starts with A |
| WHERE col IN (1, 2, 3) | Match any in list |
| WHERE col BETWEEN 10 AND 20 | Range (inclusive) |
| WHERE col IS NULL | Null check |
| ORDER BY col DESC | Sort descending |
Joins
| INNER JOIN t2 ON t1.id = t2.fk | Only matching rows |
| LEFT JOIN t2 ON t1.id = t2.fk | All left + matched right |
| RIGHT JOIN t2 ON t1.id = t2.fk | All right + matched left |
| FULL OUTER JOIN | All rows from both |
Aggregates
| COUNT(*) | Number of rows |
| SUM(col) | Sum of values |
| AVG(col) | Average value |
| MAX(col) | Highest value |
| MIN(col) | Lowest value |
| GROUP BY col | Group rows by column value |
| HAVING COUNT > 5 | Filter groups (like WHERE for aggregates) |