SQL Reference

SQL is used to create, query, update, and manage relational databases.

This section uses mostly SQL Server / T-SQL examples, with general SQL commands where the syntax is widely shared.

Default SQL Commands

Create And Use A Database

CREATE DATABASE StoreDb;
GO

USE StoreDb;
GO

Create A Table

CREATE TABLE Customers (
    CustomerId INT IDENTITY(1,1) PRIMARY KEY,
    FirstName NVARCHAR(100) NOT NULL,
    LastName NVARCHAR(100) NOT NULL,
    Email NVARCHAR(255) NULL,
    CreatedAt DATETIME2 NOT NULL DEFAULT SYSUTCDATETIME()
);

Insert Data

INSERT INTO Customers (FirstName, LastName, Email)
VALUES ('Eden', 'Example', 'eden@example.com');

Select Data

SELECT CustomerId, FirstName, LastName, Email
FROM Customers;

Filter Data

SELECT CustomerId, FirstName, LastName
FROM Customers
WHERE LastName = 'Example';

Sort Data

SELECT CustomerId, FirstName, LastName
FROM Customers
ORDER BY CreatedAt DESC;

Update Data

UPDATE Customers
SET Email = 'new-email@example.com'
WHERE CustomerId = 1;

Delete Data

DELETE FROM Customers
WHERE CustomerId = 1;

Add A Column

ALTER TABLE Customers
ADD PhoneNumber NVARCHAR(50) NULL;

Change A Column

ALTER TABLE Customers
ALTER COLUMN PhoneNumber NVARCHAR(100) NULL;

Drop A Column

ALTER TABLE Customers
DROP COLUMN PhoneNumber;

Drop A Table

DROP TABLE Customers;

Count Rows

SELECT COUNT(*) AS TotalCustomers
FROM Customers;

Group Rows

SELECT LastName, COUNT(*) AS Total
FROM Customers
GROUP BY LastName;

Filter Groups

SELECT LastName, COUNT(*) AS Total
FROM Customers
GROUP BY LastName
HAVING COUNT(*) > 1;

SQL Feature Pages

Common Query Order

SQL is written in this order:

SELECT
FROM
JOIN
WHERE
GROUP BY
HAVING
ORDER BY

SQL is logically processed closer to this order:

FROM
JOIN
WHERE
GROUP BY
HAVING
SELECT
ORDER BY

Sources

Back to Home