SQL Server Cheatsheet

Quick reference guide for SQL Server database operations

Introduction to SQL

SQL (Structured Query Language) is the standard language for managing relational databases.

SQL Command Types

DDL: Data Definition Language (CREATE, ALTER, DROP)
DML: Data Manipulation Language (INSERT, UPDATE, DELETE)
DQL: Data Query Language (SELECT)
DCL: Data Control Language (GRANT, REVOKE)
TCL: Transaction Control Language (COMMIT, ROLLBACK)

Basic Example

SELECT TOP 10 * FROM customers 
WHERE country = 'USA' 
ORDER BY last_name;

Setting Up SQL Server Environment

Installation

SQL Server Express Edition
SQL Server Management Studio (SSMS)
Azure Data Studio

Online Tools

Azure SQL Database
SQL Fiddle (SQL Server mode)
DB Fiddle (SQL Server mode)

IDEs

SQL Server Management Studio
Azure Data Studio
Visual Studio with SQL Server Data Tools
DBeaver

Schema and Table Operations

User/Schema Creation

CREATE LOGIN my_user WITH PASSWORD = 'password';
CREATE USER my_user FOR LOGIN my_user;
ALTER USER my_user WITH DEFAULT_SCHEMA = dbo;
GRANT SELECT, INSERT, UPDATE, DELETE TO my_user;

Table Creation

CREATE TABLE employees (
  id INT PRIMARY KEY IDENTITY,
  name VARCHAR(100) NOT NULL,
  email VARCHAR(100) UNIQUE,
  hire_date DATE DEFAULT GETDATE(),
  salary DECIMAL(10,2) CHECK (salary > 0)
);

CREATE SEQUENCE emp_seq START WITH 1;

Common Data Types

INT, BIGINT: Integer values
VARCHAR(n): Variable string

DATE, DATETIME: Date and time
DATETIME2: Precise date/time

CHAR(n): Fixed-length string
DECIMAL(p,s): Exact numeric

Basic SQL Queries

Filtering Data

SELECT TOP 5 product_name, price
FROM products
WHERE price > 100 
  AND category = 'Electronics'
ORDER BY price DESC;

Sorting & Limiting

SELECT * FROM customers
ORDER BY last_name ASC, 
         first_name ASC
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;

Modifying Data (DML)

INSERT

INSERT INTO employees 
(name, email, salary)
VALUES 
('John Doe', 'john@example.com', 50000);

UPDATE

UPDATE employees
SET salary = salary * 1.1
WHERE department = 'Sales';

DELETE

DELETE FROM products
WHERE discontinued = 1;

Advanced Filtering

IN, BETWEEN, LIKE

SELECT * FROM products
WHERE category IN ('Electronics', 'Books')
  AND price BETWEEN 50 AND 200
  AND product_name LIKE '%Phone%';

NULL Handling

SELECT * FROM customers
WHERE phone IS NOT NULL;

UPDATE employees
SET manager_id = NULL
WHERE manager_id = 10;

Working with Multiple Tables

INNER JOIN

SELECT o.order_id, c.customer_name
FROM orders o
INNER JOIN customers c 
  ON o.customer_id = c.customer_id;

LEFT JOIN

SELECT e.name, d.department_name
FROM employees e
LEFT JOIN departments d
  ON e.dept_id = d.dept_id;

Self Join Example

SELECT e1.name AS employee, 
       e2.name AS manager
FROM employees e1
LEFT JOIN employees e2
  ON e1.manager_id = e2.employee_id;

Aggregation and Grouping

Aggregate Functions

SELECT 
  COUNT(*) AS total_products,
  AVG(price) AS avg_price,
  MIN(price) AS min_price,
  MAX(price) AS max_price,
  SUM(stock) AS total_stock
FROM products;

GROUP BY & HAVING

SELECT department_id, 
  COUNT(*) AS emp_count,
  AVG(salary) AS avg_salary
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5
ORDER BY avg_salary DESC;

Key Differences

WHERE filters before grouping
HAVING filters after grouping
Non-aggregated columns in SELECT must be in GROUP BY
Aggregate functions can't be used in WHERE

Subqueries

Single-Row Subquery

SELECT name, salary
FROM employees
WHERE salary > (
  SELECT AVG(salary)
  FROM employees
);

Multi-Row Subquery

SELECT product_name, price
FROM products
WHERE category_id IN (
  SELECT category_id
  FROM categories
  WHERE department = 'Electronics'
);

Correlated Subquery

SELECT e.name, e.salary, e.department_id
FROM employees e
WHERE salary > (
  SELECT AVG(salary)
  FROM employees
  WHERE department_id = e.department_id
);

Views and Indexes

Creating Views

CREATE OR ALTER VIEW high_paid_employees AS
SELECT id, name, salary, department
FROM employees
WHERE salary > 100000
WITH CHECK OPTION;

SELECT * FROM high_paid_employees;

Creating Indexes

CREATE INDEX idx_employee_name 
ON employees(name);

CREATE UNIQUE INDEX idx_customer_email
ON customers(email);

CREATE INDEX idx_order_dates
ON orders(order_date, shipped_date);

Index Best Practices

Index columns frequently used in WHERE, JOIN, ORDER BY
Avoid over-indexing (slows down INSERT/UPDATE)
Consider composite indexes for multi-column queries
Monitor index usage and remove unused indexes

Basic SQL Functions

String Functions

SELECT 
  first_name + ' ' + last_name AS full_name,
  UPPER(email) AS email_upper,
  SUBSTRING(phone, 1, 3) AS area_code,
  LEN(address) AS addr_length
FROM customers;

Date Functions

SELECT 
  GETDATE() AS current_datetime,
  CAST(order_date AS DATE) AS order_date_only,
  DATEDIFF(DAY, GETDATE(), due_date) AS days_remaining,
  DATEADD(MONTH, 12, hire_date) AS anniversary
FROM orders;

Math Functions

SELECT 
  ROUND(price * 1.1, 2) AS price_with_tax,
  ABS(discount) AS absolute_discount,
  quantity % 10 AS remainder,
  CEILING(weight) AS rounded_weight
FROM products;

Transactions and ACID

Transaction Control

BEGIN TRANSACTION;

UPDATE accounts 
SET balance = balance - 100
WHERE id = 123;

UPDATE accounts 
SET balance = balance + 100
WHERE id = 456;

COMMIT TRANSACTION;
-- or ROLLBACK TRANSACTION if error occurs

ACID Properties

Atomicity: All or nothing execution
Consistency: Valid state transitions
Isolation: Concurrent transactions don't interfere
Durability: Committed changes persist

Stored Procedures & Functions

Stored Procedure

CREATE OR ALTER PROCEDURE update_salary
  @emp_id INT,
  @increase_percent DECIMAL(5,2)
AS
BEGIN
  UPDATE employees
  SET salary = salary * (1 + @increase_percent/100)
  WHERE id = @emp_id;
  
  RETURN @@ROWCOUNT;
END;
GO

EXEC update_salary @emp_id = 101, @increase_percent = 10;

Scalar Function

CREATE OR ALTER FUNCTION get_employee_age(
  @emp_id INT
) RETURNS INT
AS
BEGIN
  DECLARE @age INT;
  
  SELECT @age = DATEDIFF(YEAR, birth_date, GETDATE())
  FROM employees
  WHERE id = @emp_id;
  
  RETURN @age;
END;
GO

SELECT name, dbo.get_employee_age(id) AS age
FROM employees;

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