Question

My situation is i have four tables Patient, Receipt, Clinic and Laboratory.

 CREATE DATABASE TestHosp

 GO
 USE TestHosp
 GO

Information about patient

 CREATE TABLE Patient
 (Id INT Not NULL PRIMARY KEY IDENTITY(1,1),
 FirestName VARCHAR(12) NOT NULL,
 LastName VARCHAR(12) NOT NULL,
 Birthday DATETIME)

 CREATE TABLE Clinic
(Id INT NOT NULL PRIMARY KEY IDENTITY(1,1),
ClinicName VARCHAR(20) UNIQUE,
Price DECIMAL(8,2))

CREATE TABLE Laboratory
(Id INT NOT NULL PRIMARY KEY IDENTITY(1,1),
LaboratoryName VARCHAR(20) UNIQUE,
Price DECIMAL (8,2))

Note that the receipt contains a receipt number, One receipt belongs to one laboratory, One receipt belongs to one clinic i want do relation without create two column FK_Laboratory_ID and FK_Clinic_ID
and one number for all receipt any way to do this.

CREATE TABLE Receipt
(Id INT NOT NULL PRIMARY KEY IDENTITY(1,1),
PatientID INT NOT NULL 
CONSTRAINT [FK_Patient_ID] FOREIGN KEY (PatientID) REFERENCES Patient(Id),
DATE DATETIME,
Paid DECIMAL(8,2))

Answer 1

Your database design does not look good at all. If you could elaborate on design requirements, your schema can be very well improved.

To answer your question,

Patient (Id, FirstName, LastName, Birthday)

Clinic (Id, Name, Price)

Laboratory (Id, Name, Price)

Split your Receipt table into,

Clinic_Receipt (Id, PatientId, ClinicId)

Laboratory_Receipt (Id, PatientId, LaboratoryId)

     //Create Unique Ids for Receipts

     public int CreatId()
     {
         TimeSpan t = (DateTime.UtcNow - new DateTime(1970, 1, 1));

         return (int) t.TotalSeconds;
     }