---
title: "SQL 101"
date: 2024-04-03T00:16:10.000Z
author: Z.SHINCHVEN
tags: [SQL]
canonical: https://atlassc.net/2024/04/03/sql-101
---
**Key SQL Categories**

* **DDL (Data Definition Language):** Commands that control the structure of a database and its objects.
    * **CREATE:**  Creates databases, tables, indexes, etc.
    * **ALTER:** Modifies the structure of existing objects.
    * **DROP:**  Deletes databases, tables, and other objects.
    * **TRUNCATE:** Quickly removes all data from a table.

* **DQL (Data Query Language):** Commands for retrieving and filtering data from databases.
    * **SELECT:**  Fetches data from one or more tables. 

* **DML (Data Manipulation Language):** Commands for changing data within tables.
    * **INSERT:** Adds new rows of data to a table.
    * **UPDATE:** Modifies existing data in a table.
    * **DELETE:** Removes rows from a table.

* **DCL (Data Control Language):** Commands to manage database permissions and user access.
    * **GRANT:** Provides specific permissions to users.
    * **REVOKE:**  Removes permissions from users.

* **TCL (Transaction Control Language):** Commands for managing groups of  SQL statements as a single unit (transactions).
    * **COMMIT:**  Makes changes permanent in a database.
    * **ROLLBACK:**  Reverts changes made during a transaction.
    * **SAVEPOINT:** Sets points within a transaction to potentially roll back to.

**Operators**

* **Arithmetic Operators:** (+, -, *,  /) for calculations.
* **Comparison Operators:**  (>, <, =, >=, <=, !=) for comparing values.
* **Logical Operators:**  (AND, OR, NOT) for combining conditions.
* **Other Operators:** 
    * **LIKE:**  For pattern matching in strings.
    * **IN:** To check if a value exists within a set.
    * **BETWEEN:** To check if a value is within a range.

**Functions**

* **Aggregate Functions:**  Perform calculations on multiple rows, returning a single result:
    * **COUNT()** 
    * **MIN()**
    * **MAX()**
    * **AVG()** 
    * **SUM()**
* **String Functions:** Manipulate text data:
    * **UPPER()**
    * **LOWER()**
    * **CONCAT()**
    * **SUBSTRING()** 
    * **TRIM()** 
* **Date and Time Functions:**  Work with dates and times:
    * **NOW()**
    * **CURDATE()**
    * **MONTH()** 
    * **YEAR()** 
* **Other Functions:**  Conversion functions, mathematical functions, etc.

**Data Types**

(Data types can vary slightly between different database systems)

* **Numeric:**
    * **INT/INTEGER**  (whole numbers)
    * **FLOAT/DECIMAL** (numbers with decimal points)
* **String:**
    * **CHAR** (fixed-length strings)
    * **VARCHAR**  (variable-length strings)
    * **TEXT** (larger text fields)
* **Date and Time:**
    * **DATE** 
    * **TIME**
    * **DATETIME** 
    * **TIMESTAMP**
* **Boolean:** (TRUE or FALSE)

**How to Learn SQL**

1. **Choose a Resource:** There are many excellent options:
    * **Online Courses:** Platforms like Codecademy, Udemy, Coursera, Khan Academy.
    * **Interactive Tutorials:** W3Schools, SQLZoo, TutorialsPoint.
    * **Books:**  Books tailored to your preference.
2. **Database Choice:**  Select a common database system to practice with:
    * **MySQL**
    * **PostgreSQL**
    * **Microsoft SQL Server**
    * **SQLite**
3. **Practice, Practice, Practice:** 
    * Find datasets online or create your own simple tables.
    * Run queries, experiment, and solidify your understanding.