insert into...

On Dec 9, 2007, at 11:05 , Alain Roger wrote:

Hi,

i would like to understand why the following INSERT INTO statement
works :

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

whereas usually we should do :

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

Well, imho, if the sequence was set up via serial (or otherwise is
set as the default for the first column), I think the easiest way is :

INSERT INTO mytable (name, firstname)
VALUES ('myname', 'myfirstname');

No need to include the nextval call at all.

If you look at the INSERT synoposis:

http://www.postgresql.org/docs/8.2/static/sql-insert.html

INSERT INTO table [ ( column [, ...] ) ]
{ DEFAULT VALUES | VALUES ( { expression | DEFAULT } [, ...] )
[, ...] | query }
[ RETURNING * | output_expression [ AS output_name ] [, ...] ]

you can see that a VALUES expression or a query are legitimate forms
for INSERT. The query form is particularly useful if you'd like to
insert a number of rows that are the result of a SELECT. For example,
when loading data from a temp table.

INSERT INTO mytable (name, firstname)
SELECT name, firstname
FROM temp_table;

Michael Glaesemannn
grzm seespotcode net

Values is optional. We support insert into select

Dave
On 9-Dec-07, at 11:05 AM, Alain Roger wrote:

"Alain Roger" <raf.news@gmail.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