CREATE TABLE Locations
(
    Id int PRIMARY KEY IDENTITY,
    Latitude float NOT NULL,
    Longitude float NOT NULL
)

CREATE TABLE Credentials
(
    Id int PRIMARY KEY IDENTITY,
    Email varchar(30) NOT NULL,
    Password varchar(20) NOT NULL
)

CREATE TABLE Users
(
    Id int PRIMARY KEY IDENTITY,
    Nickname varchar(25) NOT NULL,
    Gender char(1) NOT NULL,
    Age int CHECK(Age >= 0) NOT NULL,
    LocationId int FOREIGN KEY REFERENCES Locations(Id) NOT NULL,
    CredentialId int UNIQUE FOREIGN KEY REFERENCES Credentials(Id) NOT NULL
)

CREATE TABLE Chats
(
    Id int PRIMARY KEY IDENTITY,
    Title varchar(32) NOT NULL,
    StartDate date NOT NULL,
    IsActive bit NOT NULL
)

CREATE TABLE Messages
(
    Id int PRIMARY KEY IDENTITY,
    Content varchar(200) NOT NULL,
    SentOn date NOT NULL,
    ChatId int FOREIGN KEY REFERENCES Chats(Id) NOT NULL,
    UserId int FOREIGN KEY REFERENCES Users(Id) NOT NULL
)

CREATE TABLE UsersChats
(
    UserId int FOREIGN KEY REFERENCES Users(Id) NOT NULL,
    ChatId int FOREIGN KEY REFERENCES Chats(Id) NOT NULL,
    CONSTRAINT PK_UsersChats
    PRIMARY KEY (ChatId, UserId)
)