PostgreSQL function for last inserted ID

问题:

In PostgreSQL, how do I get the last id inserted into a table?

In MS SQL there is SCOPE_IDENTITY().

Please do not advise me to use something like this:

select max(id) from table

回答1:

( tl;dr : goto option 3: INSERT with RETURNING )

Recall that in postgresql there is no \"id\" concept for tables, just sequences (which are typically but not necessarily used as default values for surrogate primary keys, with the SERIAL pseudo-type).

If you are interested in getting the id of a newly inserted row, there are several ways:

---

Option 1: CURRVAL(<sequence name>);.

For example:

  INSERT INTO persons (lastname,firstname) VALUES (\'Smith\', \'John\');
  SELECT currval(\'persons_id_seq\');

The name of the sequence must be known, it\'s really arbitrary; in this example we assume that the table persons has an id column created with the SERIAL pseudo-type. To avoid relying on this and to feel more clean, you can use instead pg_get_serial_sequence:

  INSERT INTO persons (lastname,firstname) VALUES (\'Smith\', \'John\');
  SELECT currval(pg_get_serial_sequence(\'persons\',\'id\'));

Caveat: currval() only works after an INSERT (which has executed nextval() ), in the same session.

---

Option 2: LASTVAL();

This is similar to the previous, only that you don\'t need to specify the sequence name: it looks for the most recent modified sequence (always inside your session, same caveat as above).

---

Both CURRVAL and LASTVAL are totally concurrent safe. The behaviour of sequence in PG is designed so that different session will not interfere, so there is no risk of race conditions (if another session inserts another row between my INSERT and my SELECT, I still get my correct value).

However they do have a subtle potential problem. If the database has some TRIGGER (or RULE) that, on insertion into persons table, makes some extra insertions in other tables... then LASTVAL will probably give us the wrong value. The problem can even happen with CURRVAL, if the extra insertions are done intto the same persons table (this is much less usual, but the risk still exists).

---

Option 3: INSERT with RETURNING

INSERT INTO persons (lastname,firstname) VALUES (\'Smith\', \'John\') RETURNING id;

This is the most clean, efficient and safe way to get the id. It doesn\'t have any of the risks of the previous.

Drawbacks? Almost none: you might need to modify the way you call your INSERT statement (in the worst case, perhaps your API or DB layer does not expect an INSERT to return a value); it\'s not standard SQL (who cares); it\'s available since Postgresql 8.2 (Dec 2006...)

---

Conclusion: If you can, go for option 3. Elsewhere, prefer 1.

Note: all these methods are useless if you intend to get the last globally inserted id (not necessarily in your session). For this, you must resort to select max(id) from table (of course, this will not read uncommitted inserts from other transactions).

回答2:

See the RETURNING clause of the INSERT statement. Basically, the INSERT doubles as a query and gives you back the value that was inserted.

回答3:

you can use RETURNING clause in INSERT statement,just like the following

wgzhao=# create table foo(id int,name text);
CREATE TABLE
wgzhao=# insert into foo values(1,\'wgzhao\') returning id;
 id 
----
  1
(1 row)

INSERT 0 1
wgzhao=# insert into foo values(3,\'wgzhao\') returning id;
 id 
----
  3
(1 row)

INSERT 0 1

wgzhao=# create table bar(id serial,name text);
CREATE TABLE
wgzhao=# insert into bar(name) values(\'wgzhao\') returning id;
 id 
----
  1
(1 row)

INSERT 0 1
wgzhao=# insert into bar(name) values(\'wgzhao\') returning id;
 id 
----
  2
(1 row)

INSERT 0 

回答4:

Leonbloy\'s answer is quite complete. I would only add the special case in which one needs to get the last inserted value from within a PL/pgSQL function where OPTION 3 doesn\'t fit exactly.

For example, if we have the following tables:

CREATE TABLE person(
   id serial,
   lastname character varying (50),
   firstname character varying (50),
   CONSTRAINT person_pk PRIMARY KEY (id)
);

CREATE TABLE client (
    id integer,
   CONSTRAINT client_pk PRIMARY KEY (id),
   CONSTRAINT fk_client_person FOREIGN KEY (id)
       REFERENCES person (id) MATCH SIMPLE
);

If we need to insert a client record we must refer to a person record. But let\'s say we want to devise a PL/pgSQL function that inserts a new record into client but also takes care of inserting the new person record. For that, we must use a slight variation of leonbloy\'s OPTION 3:

INSERT INTO person(lastname, firstname) 
VALUES (lastn, firstn) 
RETURNING id INTO [new_variable];

Note that there are two INTO clauses. Therefore, the PL/pgSQL function would be defined like:

CREATE OR REPLACE FUNCTION new_client(lastn character varying, firstn character varying)
  RETURNS integer AS
$BODY$
DECLARE
   v_id integer;
BEGIN
   -- Inserts the new person record and retrieves the last inserted id
   INSERT INTO person(lastname, firstname)
   VALUES (lastn, firstn)
   RETURNING id INTO v_id;

   -- Inserts the new client and references the inserted person
   INSERT INTO client(id) VALUES (v_id);

   -- Return the new id so we can use it in a select clause or return the new id into the user application
    RETURN v_id;
END;
$BODY$
  LANGUAGE plpgsql VOLATILE;

Now we can insert the new data using:

SELECT new_client(\'Smith\', \'John\');

or

SELECT * FROM new_client(\'Smith\', \'John\');

And we get the newly created id.

new_client
integer
----------
         1

回答5:

See the below example

CREATE TABLE users (
    -- make the \"id\" column a primary key; this also creates
    -- a UNIQUE constraint and a b+-tree index on the column
    id    SERIAL PRIMARY KEY,
    name  TEXT,
    age   INT4
);

INSERT INTO users (name, age) VALUES (\'Mozart\', 20);

Then for getting last inserted id use this for table \"user\" seq column name \"id\"

SELECT currval(pg_get_serial_sequence(\'users\', \'id\'));

回答6:

SELECT CURRVAL(pg_get_serial_sequence(\'my_tbl_name\',\'id_col_name\'))

You need to supply the table name and column name of course.

This will be for the current session / connection http://www.postgresql.org/docs/8.3/static/functions-sequence.html

回答7:

For the ones who need to get the all data record, you can add

returning *

to the end of your query to get the all object including the id.

回答8:

Try this:

select nextval(\'my_seq_name\');  // Returns next value

If this return 1 (or whatever is the start_value for your sequence), then reset the sequence back to the original value, passing the false flag:

select setval(\'my_seq_name\', 1, false);

Otherwise,

select setval(\'my_seq_name\', nextValue - 1, true);

This will restore the sequence value to the original state and \"setval\" will return with the sequence value you are looking for.

回答9:

Postgres has an inbuilt mechanism for the same, which in the same query returns the id or whatever you want the query to return. here is an example. Consider you have a table created which has 2 columns column1 and column2 and you want column1 to be returned after every insert.

# create table users_table(id serial not null primary key, name character varying);
CREATE TABLE
#insert into users_table(name) VALUES (\'Jon Snow\') RETURNING id;
 id 
----
  1
(1 row)

# insert into users_table(name) VALUES (\'Arya Stark\') RETURNING id;
 id 
----
  2
(1 row)

回答10:

If you just need to retrieve the last inserted id without insert anything you can use the following example

SELECT id FROM users ORDER BY id DESC LIMIT 1;

Hope can help.