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There is a Table "context". There is an autoincrement id "context_id". I am using sequence to retrieve the next value.

SELECT nextval('context_context_id_seq')

The result is: 1, 2, 3,...20....

But there are 24780 rows in the "context" table

How can I get the next value (24781)?

I need to use it in the INSERT statement

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Apparently you inserted rows into that table without using the sequence and that's why they are out of sync.

You need to set the correct value for the sequence using setval()

select setval('context_context_id_seq', (select max(context_id) from context));

Then the next call to nextval() should return the correct value.

If the column is indeed defined as serial (there is no "auto increment" in Postgres) then you should let Postgres do it's job and never mention it during insers:

insert into context (some_column, some_other_column)
values (42, 'foobar');

will make sure the default value for the context_id column is applied. Alternatively you could use:

insert into context (context_id, some_column, some_other_column)
values (default, 42, 'foobar');
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and when using serial count still can jump over 1 or 2 id's. That because postgresql first takes nextval then tries to insert and if it fails for somereason that id is already used – simplexio May 22 '14 at 9:43
@user503207: a sequence is never guaranteed to be gap-free. – a_horse_with_no_name May 22 '14 at 9:43
Autoincrement fields, sequences, serials, identity whatever you want to call them, generally have a caching mechanism which means that strictly linear gap-free monotonically increasing sequences of integers are impossible to guarantee. – Vérace May 22 '14 at 11:50

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