Question

What is the difference between using

SELECT ... INTO MyTable FROM...

and

INSERT INTO MyTable (...)
SELECT ... FROM ....

?

From BOL [ INSERT, SELECT…INTO ], I know that using SELECT…INTO will create the insertion table on the default file group if it doesn’t already exist, and that the logging for this statement depends on the recovery model of the database.

1. Which statement is preferable?
2. Are there other performance implications?
3. What is a good use case for SELECT…INTO over INSERT INTO …?

Edit: I already stated that I know that that SELECT INTO… creates a table where it doesn’t exist. What I want to know is that SQL includes this statement for a reason, what is it? Is it doing something different behind the scenes for inserting rows, or is it just syntactic sugar on top of a CREATE TABLE and INSERT INTO.

Answer 1

1. They do different things. Use INSERT when the table exists. Use SELECT INTO when it does not.

2. Yes. INSERT with no table hints is normally logged. SELECT INTO is minimally logged assuming proper trace flags are set.

3. In my experience SELECT INTO is most commonly used with intermediate data sets, like #temp tables, or to copy out an entire table like for a backup. INSERT INTO is used when you insert into an existing table with a known structure.

EDIT

To address your edit, they do different things. If you are making a table and want to define the structure use CREATE TABLE and INSERT. Example of an issue that can be created: You have a small table with a varchar field. The largest string in your table now is 12 bytes. Your real data set will need up to 200 bytes. If you do SELECT INTO from your small table to make a new one, the later INSERT will fail with a truncation error because your fields are too small.