Postgres manually alter sequence

问题

I\'m trying to set a sequence to a specific value.

SELECT setval(\'payments_id_seq\'), 21, true

This gives an error:

ERROR: function setval(unknown) does not exist

Using ALTER SEQUENCE doesn\'t seem to work either?

ALTER SEQUENCE payments_id_seq LASTVALUE 22

How can this be done?

Ref: https://www.postgresql.org/docs/current/static/functions-sequence.html

回答1:

The parentheses are misplaced:

SELECT setval('payments_id_seq', 21, true);  # next value will be 22

Otherwise you're calling setval with a single argument, while it requires two or three.

回答2:

This syntax isn't valid in any version of PostgreSQL:

ALTER SEQUENCE payments_id_seq LASTVALUE 22

This would work:

ALTER SEQUENCE payments_id_seq RESTART WITH 22;

and is equivalent to:

SELECT setval('payments_id_seq', 22, FALSE);

More in the current manual for ALTER SEQUENCE and sequence functions.

Note that setval() expects either (regclass, bigint) or (regclass, bigint, boolean). In the above example I am providing untyped literals. That works too. But if you feed typed variables to the function you may need explicit type casts to satisfy function type resolution. Like:

SELECT setval(my_text_variable::regclass, my_other_variable::bigint, FALSE);

---

For repeated operations you might be interested in:

ALTER SEQUENCE payments_id_seq START WITH 22; -- set default
ALTER SEQUENCE payments_id_seq RESTART;       -- without value

START [WITH] stores a default RESTART number, which is used for subsequent RESTART calls without value. You need Postgres 8.4 or later for the last part.

回答3:

Use select setval('payments_id_seq', 21, true);

setval contains 3 parameters:

• 1st parameter is sequence_name
• 2nd parameter is Next nextval
• 3rd parameter is optional.

The use of true or false in 3rd parameter of setval is as follows:

SELECT setval('payments_id_seq', 21);           // Next nextval will return 22
SELECT setval('payments_id_seq', 21, true);     // Same as above 
SELECT setval('payments_id_seq', 21, false);    // Next nextval will return 21

The better way to avoid hard-coding of sequence name, next sequence value and to handle empty column table correctly, you can use the below way:

SELECT setval(pg_get_serial_sequence('table_name', 'id'), coalesce(max(id), 0)+1 , false) FROM table_name;

where table_name is the name of the table, id is the primary key of the table

回答4:

setval('sequence_name', sequence_value)

来源：https://stackoverflow.com/questions/8745051/postgres-manually-alter-sequence