using System;

using System.Collections.Generic;

using System.Linq;

 using System.Text.RegularExpressions;

public class Program

{

​

    public static void Main()

    {

        string reg1 = "[dl].[Table]";

        bool reg1Valid = IsValid(reg1);

        Console.WriteLine($"reg1 isValid {IsValid(reg1)}");

             bool  IsValid(string  value ){

        return  !Regex.IsMatch((string)value, @"^(\[dl]\.\[\w+]( FOR SYSTEM_TIME AS OF N'(\d|-|\s|:|\.)+')?)( JOIN \[dl]\.\[\w+]( FOR SYSTEM_TIME AS OF N'(\d|-|\s|:|\.)+')? ON \[dl]\.\[\w+]\.\[\w+]\s*=\s*\[dl]\.\[\w+]\.\[\w+])*", RegexOptions.IgnoreCase);

    }

    }

​

}