How can I INSERT data into two tables simultaneously in SQL Server?

Question

Let's say my table structure looks something like this:

CREATE TABLE [dbo].[table1] (
    [id] [int] IDENTITY(1,1) NOT NULL,
    [data] [varchar](255) NOT NULL,
    CONSTRAINT [PK_table1] PRIMARY KEY CLUSTERED ([id] ASC)
)

CREATE TABLE [dbo].[table2] (
    [id] [int] IDENTITY(1,1) NOT NULL,
    [table1_id] [int] NOT NULL,
    [data] [varchar](255) NOT NULL,
    CONSTRAINT [PK_table2] PRIMARY KEY CLUSTERED ([id] ASC)
)

The [id] field of the first table corresponds to the [table1_id] field of the second. What I would like to do is insert data into both tables in a single transaction. Now I already know how to do this by doing INSERT-SELECT-INSERT, like this:

BEGIN TRANSACTION;
DECLARE @id [int];
INSERT INTO [table1] ([data]) VALUES ('row 1');
SELECT @id = SCOPE_IDENTITY();
INSERT INTO [table2] ([table1_id], [data]) VALUES (@id, 'more of row 1');
COMMIT TRANSACTION;

That's all good and fine for small cases like that where you're only inserting maybe a handful of rows. But what I need to do is insert a couple hundred thousand rows, or possibly even a million rows, all at once. The data is coming from another table, so if I was only inserting it into a single table, it would be easy, I'd just have to do this:

INSERT INTO [table] ([data])
SELECT [data] FROM [external_table];

But how would I do this and split the data into [table1] and [table2], and still update [table2] with the appropriate [table1_id] as I'm doing it? Is that even possible?

Answer 1

Try this:

insert into [table] ([data])
output inserted.id, inserted.data into table2
select [data] from [external_table]

UPDATE: Re:

Denis - this seems very close to what I want to do, but perhaps you could fix the following SQL statement for me? Basically the [data] in [table1] and the [data] in [table2] represent two different/distinct columns from [external_table]. The statement you posted above only works when you want the [data] columns to be the same.

INSERT INTO [table1] ([data]) 
OUTPUT [inserted].[id], [external_table].[col2] 
INTO [table2] SELECT [col1] 
FROM [external_table] 

It's impossible to output external columns in an insert statement, so I think you could do something like this

merge into [table1] as t
using [external_table] as s
on 1=0 --modify this predicate as necessary
when not matched then insert (data)
values (s.[col1])
output inserted.id, s.[col2] into [table2]
;