Re: insert into...

>
"Alain Roger" <raf(dot)news(at)gmail(dot)com> writes:
> i would like to understand why the following INSERT INTO statement works :

> INSERT INTO mytable
> SELECT nextval('my_sequence'),
> 'myname',
> 'myfirstname'
> ;

This is a perfectly standard INSERT ... SELECT query.

> whereas usually we should do :

> INSERT INTO mytable
> VALUES
> (
> SELECT nextval('my_sequence'),
> 'myname',
> 'myfirstname'
> );

If you'd tried that, you would find that it *does not* work:

regression=# INSERT INTO mytable
regression-# VALUES
regression-# (
regression(# SELECT nextval('my_sequence'),
regression(# 'myname',
regression(# 'myfirstname'
regression(# );
ERROR: syntax error at or near "SELECT"
LINE 4: SELECT nextval('my_sequence'),
^

You could make it work by turning the SELECT into a parenthesized
sub-SELECT:

INSERT INTO mytable
VALUES
(
(SELECT nextval('my_sequence')),
'myname',
'myfirstname'
);

but this is just pointless complexity. The standard idiom is

INSERT INTO mytable
VALUES
(
nextval('my_sequence'),
'myname',
'myfirstname'
);

or as already noted, leave out the column entirely and rely on
the default expression.

regards, tom lane