SELECT |
Retrieve data from database |
SELECT * FROM Customers; |
INSERT INTO |
Insert new records into table |
INSERT INTO Customers VALUES (1, 'John'); |
UPDATE |
Update existing records |
UPDATE Customers SET name='Jane' WHERE id=1; |
DELETE |
Delete records from table |
DELETE FROM Customers WHERE id=1; |
WHERE |
Filter records based on condition |
SELECT * FROM Customers WHERE age > 18; |
ORDER BY |
Sort result set |
SELECT * FROM Customers ORDER BY name; |
JOIN |
Combine rows from multiple tables |
SELECT * FROM Orders JOIN Customers ON Orders.customer_id = Customers.id; |
INNER JOIN |
Returns matching records from both tables |
SELECT * FROM A INNER JOIN B ON A.id = B.id; |
LEFT JOIN |
Returns all records from left table and matching from right |
SELECT * FROM A LEFT JOIN B ON A.id = B.id; |
GROUP BY |
Group rows that have same values |
SELECT category, COUNT(*) FROM Products GROUP BY category; |
HAVING |
Filter groups (used with GROUP BY) |
SELECT category, COUNT(*) FROM Products GROUP BY category HAVING COUNT(*) > 5; |
CREATE TABLE |
Create a new table |
CREATE TABLE Customers (id INT, name VARCHAR(100)); |
ALTER TABLE |
Modify table structure |
ALTER TABLE Customers ADD email VARCHAR(100); |
DROP TABLE |
Delete a table |
DROP TABLE Customers; |
PRIMARY KEY |
Uniquely identifies each row |
CREATE TABLE Customers (id INT PRIMARY KEY, name VARCHAR(100)); |
FOREIGN KEY |
References primary key in another table |
FOREIGN KEY (customer_id) REFERENCES Customers(id); |
COUNT() |
Count number of rows |
SELECT COUNT(*) FROM Customers; |
SUM() |
Sum of numeric column |
SELECT SUM(price) FROM Orders; |
AVG() |
Average of numeric column |
SELECT AVG(price) FROM Products; |
MIN() |
Minimum value in column |
SELECT MIN(price) FROM Products; |
MAX() |
Maximum value in column |
SELECT MAX(price) FROM Products; |