added table of contents

Author: shayandelbari

sql-command-summary.md

@@ -1,5 +1,73 @@
 # SQL Commands Summary
 
+## Table of Contents
+
+- [Data Retrieval](#data-retrieval)
+  - [SELECT](#1-select)
+  - [CREATE VIEW](#2-create-view)
+  - [GROUP BY](#3-group-by)
+  - [HAVING](#4-having)
+- [Data Manipulation](#data-manipulation)
+  - [INSERT](#5-insert)
+  - [UPDATE](#6-update)
+  - [DELETE](#7-delete)
+- [Data Definition](#data-definition)
+  - [CREATE TABLE](#8-create-table)
+  - [ALTER TABLE](#9-alter-table)
+  - [DROP TABLE](#10-drop-table)
+- [Constraints](#constraints)
+  - [PRIMARY KEY](#11-primary-key)
+  - [FOREIGN KEY](#12-foreign-key)
+  - [UNIQUE](#13-unique)
+  - [CHECK](#14-check)
+  - [NOT NULL](#15-not-null)
+- [Transactions](#transactions)
+  - [SAVEPOINT](#16-savepoint)
+  - [ROLLBACK](#17-rollback)
+  - [COMMIT](#18-commit)
+- [User Management](#user-management)
+  - [CREATE USER](#19-create-user)
+  - [GRANT](#20-grant)
+  - [DROP USER](#21-drop-user)
+  - [ALTER USER](#22-alter-user)
+- [Sequences](#sequences)
+  - [CREATE SEQUENCE](#23-create-sequence)
+  - [NEXTVAL / CURRVAL](#24-nextval--currval)
+  - [ALTER SEQUENCE](#25-alter-sequence)
+- [Views](#views)
+  - [CREATE OR REPLACE VIEW](#26-create-or-replace-view)
+  - [WITH READ ONLY](#27-with-read-only)
+  - [WITH CHECK OPTION](#28-with-check-option)
+  - [FORCE VIEW](#29-force-view)
+- [String Functions](#string-functions)
+  - [SUBSTR](#30-substr)
+  - [UPPER / LOWER / INITCAP](#31-upper--lower--initcap)
+  - [REPLACE](#32-replace)
+  - [LPAD / RPAD](#33-lpad--rpad)
+  - [LTRIM / RTRIM](#34-ltrim--rtrim)
+  - [LENGTH](#35-length)
+- [Mathematical Functions](#mathematical-functions)
+  - [MOD](#36-mod)
+  - [POWER](#37-power)
+  - [ABS / CEIL / FLOOR](#38-abs--ceil--floor)
+  - [ROUND](#39-round)
+- [Date Functions](#date-functions)
+  - [ADD_MONTHS](#40-add_months)
+  - [LAST_DAY](#41-last_day)
+  - [MONTHS_BETWEEN](#42-months_between)
+  - [INTERVAL](#43-interval)
+  - [TO_CHAR](#44-to_char)
+- [Miscellaneous](#miscellaneous)
+  - [IS NULL / IS NOT NULL](#45-is-null--is-not-null)
+  - [NVL](#46-nvl)
+  - [NVL2](#47-nvl2)
+  - [SPOOL](#48-spool)
+  - [COUNT](#49-count)
+  - [MAX / MIN / AVG / SUM](#50-max--min--avg--sum)
+  - [ORDER BY](#51-order-by)
+  - [LIKE](#52-like)
+  - [JOIN](#53-join)
+
 ## Data Retrieval
 
 ### 1. SELECT