SQL Basics Cheat Sheet
Essential commands for interacting with relational databases.
Data Query Language (DQL)
SELECT
Select all columns from a table.
SELECT * FROM table_name;SELECT DISTINCT
Select only unique values.
SELECT DISTINCT column FROM table;WHERE
Filter records.
SELECT * FROM table WHERE condition;ORDER BY
Sort the result set.
SELECT * FROM table ORDER BY column ASC|DESC;Data Manipulation Language (DML)
INSERT INTO
Insert new records.
INSERT INTO table (col1, col2) VALUES (val1, val2);UPDATE
Modify existing records.
UPDATE table SET col1 = val1 WHERE condition;DELETE
Delete existing records.
DELETE FROM table WHERE condition;Joins
INNER JOIN
Returns records that have matching values in both tables.
SELECT * FROM t1 INNER JOIN t2 ON t1.id = t2.id;LEFT JOIN
Returns all records from the left table, and the matched records from the right table.
SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.id;Aggregation
COUNT
Returns the number of rows.
SELECT COUNT(column) FROM table;SUM
Returns the total sum of a numeric column.
SELECT SUM(column) FROM table;AVG
Returns the average value of a numeric column.
SELECT AVG(column) FROM table;GROUP BY
Group rows that have the same values.
SELECT col, COUNT(*) FROM table GROUP BY col;