CREATE TABLE Categories(
    Id INT PRIMARY KEY IDENTITY,
    [Name] NVARCHAR(30) NOT NULL
)

CREATE TABLE Items(
    Id INT PRIMARY KEY IDENTITY,
    [Name] NVARCHAR(30) NOT NULL,
    Price DECIMAL(15,2) NOT NULL,
    CategoryId INT FOREIGN KEY REFERENCES Categories(Id) NOT NULL
)

CREATE TABLE Employees(
    Id INT PRIMARY KEY IDENTITY,
    FirstName NVARCHAR(50) NOT NULL,
    LastName NVARCHAR(50) NOT NULL,
    Phone CHAR(12) NOT NULL,
    Salary DECIMAL(15,2) NOT NULL
)

CREATE TABLE Orders(
    Id INT PRIMARY KEY IDENTITY,
    [DateTime] DATETIME NOT NULL,
    EmployeeId INT FOREIGN KEY REFERENCES Employees(Id) NOT NULL
)

CREATE TABLE OrderItems(
    OrderId INT FOREIGN KEY REFERENCES Orders(Id) NOT NULL,
    ItemId INT FOREIGN KEY REFERENCES Items(Id) NOT NULL,
    Quantity INT NOT NULL CHECK(Quantity>=1)
    CONSTRAINT PK_OrderItems PRIMARY KEY (OrderId, ItemId)
)

CREATE TABLE Shifts(
    Id INT IDENTITY NOT NULL,
    EmployeeId INT FOREIGN KEY REFERENCES Employees(Id) NOT NULL,
    CheckIn DATETIME NOT NULL,
    CheckOut DATETIME NOT NULL,
    PRIMARY KEY(Id, EmployeeId)
)

ALTER TABLE Shifts
ADD CONSTRAINT CHK_CheckDates CHECK(CheckIn < CheckOut)