Обсуждение: insert into...

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'
);


thanks a lot,

--
Alain
------------------------------------
Windows XP SP2
PostgreSQL 8.2.4 / MS SQL server 2005
Apache 2.2.4
PHP 5.2.4
C# 2005-2008

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:

> 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'
> );
>
>
> thanks a lot,
>
> --
> Alain
> ------------------------------------
> Windows XP SP2
> PostgreSQL 8.2.4 / MS SQL server 2005
> Apache 2.2.4
> PHP 5.2.4
> C# 2005-2008

>
"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