Check out example codes for "wix installer create database if not exists". It will help you in understanding the concepts better.

Code Example 1

public static ActionResult CreateDatabaseXyz (Session session)
        {
            try
            {
                var builder = new SqlConnectionStringBuilder
                {
                    DataSource = session["DATABASE_SERVER"],
                    InitialCatalog = "master",
                    ConnectTimeout = 5
                };

                if (session["DATABASE_LOGON_TYPE"] != "DatabaseIntegratedAuth")
                {
                    builder.UserID = session["DATABASE_USERNAME"];
                    builder.Password = session["DATABASE_PASSWORD"];
                }
                else
                {
                    builder.IntegratedSecurity = true;
                }

                SqlCommand cmd = null;
                using (var connection = new SqlConnection(builder.ConnectionString))
                {
                    connection.Open();
                    using (cmd = new SqlCommand($"If(db_id(N'{session["DATABASE_NAME"]}') IS NULL) CREATE DATABASE [{session["DATABASE_NAME"]}]", connection))
                    {
                        cmd.ExecuteNonQuery();
                    }
                }
                session.Log("VerifySqlConnection: Ende");
            }
            catch (Exception ex)
            {
                session.Log("VerifySqlConnection: exception: {0}", ex.Message);
                throw;
            }
            return ActionResult.Success;
        }

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