📘 SQL Learning Guide (Structured Query Language)

A comprehensive learning resource to help you master SQL using Microsoft SQL Server. It includes commands, syntax explanations, and practical examples — with bilingual comments in English and Arabic.

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📂 Topics Covered

✅ SQL Basics

• Single-line (--) and multi-line (/* ... */) comments
• Data Types:
  • Numeric: int, float, money, etc.
  • String: char, varchar, nvarchar
  • DateTime: date, time, datetime
  • Binary: binary, image (deprecated)
  • Others: xml, sql_variant

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🏗️ DDL – Data Definition Language

CREATE DATABASE CompanyCycle9;
USE CompanyCycle9;

CREATE TABLE Employee (
    SSN INT PRIMARY KEY IDENTITY(1,1),
    Name VARCHAR(15) NOT NULL,
    Address VARCHAR(50) DEFAULT 'Cairo',
    Salary MONEY,
    Date DATE,
    Gender CHAR(1),
    LName VARCHAR(15),
    SuperSSN INT REFERENCES Employee(SSN),
    DNo INT
);

• ALTER TABLE, DROP TABLE supported
• Identity, Foreign Key, and NOT NULL constraints explained

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🧾 DML – Data Manipulation Language

INSERT INTO Employee (Name, LName, Date, Address, Gender, DNo, SuperSSN, Salary)
VALUES ('Amr', 'Nabih', '2003-23-08', 'Mansoura', 'M', 8, NULL, NULL);

UPDATE Employee
SET Address = 'Dokki'
WHERE SSN = 1;

DELETE FROM Employee
WHERE SSN = 9;

• Examples for inserting single and multiple rows
• Conditional updates and deletions

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🔍 DQL – Data Query Language

SELECT * FROM Student;

SELECT St_name + ' ' + St_Lname AS FullName
FROM Student;

SELECT * FROM Student
WHERE St_age BETWEEN 20 AND 25;

SELECT * FROM Student
WHERE St_address IN ('Cairo', 'Giza');

• WHERE, BETWEEN, IN, LIKE, IS NULL
• Sorting with ORDER BY, DISTINCT

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🔗 JOINS

-- INNER JOIN
SELECT S.St_name, D.Dept_Name
FROM Student S
INNER JOIN Department D ON D.Dept_Id = S.Dept_Id;

-- LEFT OUTER JOIN
SELECT S.St_name, D.Dept_Name
FROM Student S
LEFT OUTER JOIN Department D ON D.Dept_Id = S.Dept_Id;

• All join types: INNER, LEFT, RIGHT, FULL, SELF

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🧠 Subqueries

SELECT * FROM Student
WHERE St_age > (SELECT AVG(St_age) FROM Student);

• Subqueries in WHERE, IN, and DELETE statements
• Rewriting joins with subqueries

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📊 Functions

Aggregate:

SELECT COUNT(*), SUM(Salary), AVG(Salary)
FROM Instructor;

String:

SELECT LOWER(St_name), UPPER(St_Lname)
FROM Student;

DateTime:

SELECT FORMAT(GETDATE(), 'dd-MM-yyyy');
SELECT EOMONTH(GETDATE());

Null-handling:

SELECT ISNULL(St_address, 'No Address') FROM Student;
SELECT COALESCE(St_name, St_Lname, 'Unknown') FROM Student;

Ranking:

SELECT Ins_Name, Salary,
    ROW_NUMBER() OVER (ORDER BY Salary DESC) AS RNum,
    RANK() OVER (ORDER BY Salary DESC) AS Rnk,
    DENSE_RANK() OVER (ORDER BY Salary DESC) AS DRnk
FROM Instructor;

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💡 Notes

• All commands tested on Microsoft SQL Server
• Bilingual comments and examples included (English + Arabic)
• Useful for both class notes and revision

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📌 How to Use

1. Open SQL Server Management Studio (SSMS)
2. Copy each code block and run it interactively
3. Modify and explore results for better understanding