Add columns from one to another table dynamically in SQL Server - sql

Question

I have 2 tables, A and B. Table A has columns Q1, Q2, Q3, Q4 and Table B has columns Q1 and Q2 along with others. In Table A, columns will get changed in future with Q5, Q6, Q7 etc. I want to write dynamic SQL to alter the table B (adding new columns) whenever new columns are added to Table A. Columns which will get added always be like Q1, Q2,Q3...Q40.
example of my tables:
create table tableA
(
[sid] [varchar](50) not null,
[rid] [varchar](50) not null,
[Q_URL] [varchar](500) null,
[Q1] int null,
[Q2] int null,
[Q3] int null,
[Q4] int null
);
create table tableB
(
[s_id] [varchar](50) not null,
[rid] [varchar](50) not null,
[Q_URL] [varchar](500) null,
[Q1] int null,
[Q2] int null
);

Answer 1

if object_id('tempdb..#source_col') is not null
drop table #source_col
Select distinct column_name as source_r_column from hr.INFORMATION_SCHEMA.COLUMNS
where table_name = 'tableA'
and column_name like 'Q%'
and column_name <> 'Q_URL';
if object_id('tempdb..#destination_col') is not null
drop table #source_col
Select distinct column_name as source_r_column from hr.INFORMATION_SCHEMA.COLUMNS
where table_name = 'tableB'
and column_name like 'Q%'
and column_name <> 'Q_URL';
if object_id('tempdb..#newcols') is not null
drop table #newcols
Select row_number() over(order by t1.source_q_columns) as colnum,t1.source_q_columns, 'int' as datatype
into #newcols
from #tableA t1
left join #tableB t2 on t1.source_q_columns= t2.destination_q_columns
where t2.destination_q_columns is null;
Declare #sql nvarchar(max)
Declare #column varchar(10)
Declare #datatype varchar(10)
Declare #max_colnum int
set #max_colnum = (select max(colnum) from #newcols)
While(#max_colnum != 0)
begin
set #column = (select source_q_columns from #newcols where colnum = #max_colnum)
print #column
select #sql = 'Alter Table destination Add '+ #column + ' int null'
print #sql
EXEC (#sql)
set #max_colnum = #max_colnum -1
end
This is what i came up. I believe this will work for any case. :)

Answer 2

You can create something called a DDL Trigger for Alter Table event. The Trigger is created on the database level so it will fire for any Alter table commands executed on the database.
A sample of DDL trigger for Alter table event on the database level for TableA would look something like this.
CREATE TRIGGER tr_Replicate_DDL_For_TableA
ON DATABASE
FOR ALTER_TABLE
AS
BEGIN
SET NOCOUNT ON;
Declare #data xml = EVENTDATA()
,#TableName SYSNAME
,#Sql NVARCHAR(MAX);
SET #TableName = #data.value('(/EVENT_INSTANCE/ObjectName)[1]', 'SYSNAME');
SET #Sql = #data.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'nvarchar(max)');
IF (#TableName = 'TableA') --<-- only replicate changes if TableA's schema changed.
BEGIN
SET #sql = REPLACE(#sql , 'TableA' , 'TableB');
Exec sp_executesql #sql;
END
END
GO