SELECT INTO question - Mailing list pgsql-general

Hi,

We’re trying to understand what happened with a SELECT INTO. The problem can be see with this example:

# create table t1 (id int, v int);

CREATE TABLE

# insert into t1 (select x, x from generate_series(1, 5) as g(x));

INSERT 0 5

# select * from t1;

id | v

----+----

  1 |  1

  2 |  2

  3 |  3

  4 |  4

  5 |  5

(5 rows)

nms=# select into t2 from t1;

SELECT 5

# select * from t2;

--

(5 rows)

# select * into t3 from t1;

SELECT 5

# select * from t3;

id | v

----+----

  1 |  1

  2 |  2

  3 |  3

  4 |  4

  5 |  5

(5 rows)

As you can see on the first select into, the result in t2 is … missing, no “data” at all, unlike t3 which was the expected answer. Upon closer inspection, it was realized that the “expression” in the statement was left out (oops!), but instead of getting a syntax error, it worked.

So why did it work and why was nothing stored?

The only answer I’ve been able to come up with is that the expression was evaluated as a “null expression” for each row, so it gave us 5 null rows. A small part of my brain understands that, but most of my brain goes “what?!”

I’ve noticed that I can also do:

# select from t1;

--

(5 rows)

That also doesn’t make sense and yet it does in a weird way. I suspect the answer revolves around some corner case in the SQL Standard.

So, what’s going on here?

Thanks,

Kevin