Create a new column for a table with select data from another table

I have a SQL table that shows the date and time information of a topic.

FirstTable looks like this:

id	DateP	TimeP
1	1397/01/02	01:30
2	1398/05/09	05:30
3	1398/06/07	05:10
4	1398/08/09	06:12
5	1399/02/01	07:15

I want to create columns for another table that are the result of selecting the DateP column and the TimeP column from FirstTable.

SecondTable looks like this:

id	EmployeeID	1397/01/02_01:30	1398/05/09_05:30	1398/06/07_05:10	1398/08/09_06:12	1399/02/01_07:15

DECLARE @i INT = 0;
DECLARE @DatTim NVARCHAR(50)='';
SELECT @count=  Count(*) FROM FirstTable

WHILE @i <= @count
BEGIN
    @DatTim=(select DateP+TimeP FROM FirstTable where id=@i)   
    ALTER TABLE SecondTable ADD @DatTim NVARCHAR(50);
    SET @i = @i + 1;
END

Please guide me in finding the SQL code.

Answer

DECLARE @i INT = 1;
DECLARE @count INT = 0;
DECLARE @DatTim NVARCHAR(50)='';
Set @count=(select Count(*) FROM FirstTable)

WHILE @i <= @count
BEGIN
    Set @DatTim=(select ISNULL(DateP,'') + '_'+ISNULL(TimeP,'') FROM FirstTable where id=@i)   
    exec ('ALTER TABLE SecondTable ADD ['+@DatTim +'] int NULL')
    SET @i = @i + 1;
END