Need Database Table Structure for Chat Application in SQL Server

could you please refer Tuhin Paul approach since it has loosen and extendable approach

A database schema for a chat application in SQL Server:
 

CREATE TABLE Users (
  UserId INT PRIMARY KEY,
  Username VARCHAR(255) NOT NULL
);

CREATE TABLE Conversations (
  ConversationId INT PRIMARY KEY,
  CreatedAt DATETIME NOT NULL,
  Name VARCHAR(255) NULL
);

CREATE TABLE UserConversations (
  UserId INT NOT NULL,
  ConversationId INT NOT NULL,
  PRIMARY KEY (UserId, ConversationId),
  FOREIGN KEY (UserId) REFERENCES Users(UserId),
  FOREIGN KEY (ConversationId) REFERENCES Conversations(ConversationId)
);

CREATE TABLE Messages (
  MessageId INT PRIMARY KEY,
  ConversationId INT NOT NULL,
  SenderId INT NOT NULL,
  Content VARCHAR(MAX) NOT NULL,
  SentAt DATETIME NOT NULL,
  FOREIGN KEY (ConversationId) REFERENCES Conversations(ConversationId),
  FOREIGN KEY (SenderId) REFERENCES Users(UserId)
);

CREATE TABLE Groups (
  GroupId INT PRIMARY KEY,
  Name VARCHAR(255) NOT NULL
);

CREATE TABLE GroupMembers (
  GroupId INT NOT NULL,
  UserId INT NOT NULL,
  PRIMARY KEY (GroupId, UserId),
  FOREIGN KEY (GroupId) REFERENCES Groups(GroupId),
  FOREIGN KEY (UserId) REFERENCES Users(UserId)
);

CREATE TABLE GroupMessages (
  MessageId INT PRIMARY KEY,
  GroupId INT NOT NULL,
  SenderId INT NOT NULL,
  Content VARCHAR(MAX) NOT NULL,
  SentAt DATETIME NOT NULL,
  FOREIGN KEY (GroupId) REFERENCES Groups(GroupId),
  FOREIGN KEY (SenderId) REFERENCES Users(UserId)
);

In this schema, the Users table stores information about each user, and the Conversations table stores information about each conversation (e.g. one-to-one chat or group chat). The UserConversations table is a many-to-many relationship between users and conversations, allowing multiple users to participate in the same conversation.

The Messages table stores individual messages sent in one-to-one conversations, while the GroupMessages table stores messages sent in group chats. Both tables have foreign keys to the Conversations table and the Users table, so it's easy to retrieve the conversation and sender information for each message.

Finally, the Groups table stores information about each group, and the GroupMembers table is a many-to-many relationship between groups and users, allowing multiple users to belong to the same group.

Of course, this is just one example of a database schema for a chat application, and your specific requirements may vary. 

Atleast you need four table for a chat application
Users table: This table will store information about the users of the chat application.
Conversations table: This table will store information about the conversations between the users.
Participants table: This table will store the participants in each conversation.
Messages table: This table will store the messages sent in each conversation.

CREATE TABLE Users (
  UserId INT PRIMARY KEY IDENTITY(1, 1),
  UserName VARCHAR(50) NOT NULL,
  Email VARCHAR(100) NOT NULL,
  Password VARCHAR(50) NOT NULL,
  CreatedOn DATETIME NOT NULL DEFAULT GETDATE(),
  LastLoginOn DATETIME
);

CREATE TABLE Conversations (
  ConversationId INT PRIMARY KEY IDENTITY(1, 1),
  CreatedOn DATETIME NOT NULL DEFAULT GETDATE()
);

CREATE TABLE Participants (
  ParticipantId INT PRIMARY KEY IDENTITY(1, 1),
  UserId INT NOT NULL,
  ConversationId INT NOT NULL,
  FOREIGN KEY (UserId) REFERENCES Users(UserId),
  FOREIGN KEY (ConversationId) REFERENCES Conversations(ConversationId)
);

CREATE TABLE Messages (
  MessageId INT PRIMARY KEY IDENTITY(1, 1),
  ConversationId INT NOT NULL,
  SenderId INT NOT NULL,
  MessageText VARCHAR(MAX) NOT NULL,
  SentOn DATETIME NOT NULL DEFAULT GETDATE(),
  FOREIGN KEY (ConversationId) REFERENCES Conversations(ConversationId),
  FOREIGN KEY (SenderId) REFERENCES Users(UserId)
);

Please refer this one which may help you to get more idea,

https://github.com/tinode/chat/blob/master/server/db/mysql/schema.sql

https://dba.stackexchange.com/questions/192172/how-to-create-a-flexible-table-schema-for-storing-messages-from-different-chats