I have two tables in this scenario. One is my "hot sync" table which is near-realtime bi-directional sync of data from my Salesforce Org to a Postgres table. As data changes in the source system (Salesforce), it updates that table on Postgres.
On this table in Postgres, I have a trigger that runs some logic. It basically checks to see if the record triggering it has a sent date that meets some business logic, copy that row into another schema/table to "archive" it.
This all works fine.
What I need to do however is once this row has been copied into the other table, I need to update the status of the record hot sync table. Since it is bi-directional, this will allow the data in Salesforce to reflect the changes I make from the Postgres side.
Can I place this update statement within the originating trigger or is this going to cause recursion issues?
CREATE FUNCTION salesforce.archivelogicfunc()
RETURNS trigger
LANGUAGE 'plpgsql'
COST 100
VOLATILE NOT LEAKPROOF
AS $BODY$ BEGIN
IF (DATE(NEW.et4ae5__datesent__c) < NOW() - INTERVAL '180 days'
AND DATE(NEW.et4ae5__datesent__c) > NOW() - INTERVAL '540 days')
THEN
INSERT INTO archive.individualemailresult__c
(dateopened__c,
numberoftotalclicks__c,
datebounced__c,
fromname__c,
hardbounce__c,
fromaddress__c,
softbounce__c,
name,
lastmodifieddate,
opened__c,
ownerid,
subjectline__c,
isdeleted,
contact__c,
systemmodstamp,
lastmodifiedbyid,
datesent__c,
dateunsubscribed__c,
createddate,
createdbyid,
lead__c,
tracking_as_of__c,
numberofuniqueclicks__c,
senddefinition__c,
mergeid__c,
triggeredsenddefinition__c,
sfid,
id,
_hc_lastop,
_hc_err,
isarchived)
VALUES
(NEW.et4ae5__dateopened__c,
NEW.et4ae5__numberoftotalclicks__c,
NEW.et4ae5__datebounced__c,
NEW.et4ae5__fromname__c,
NEW.et4ae5__hardbounce__c,
NEW.et4ae5__fromaddress__c,
NEW.et4ae5__softbounce__c,
NEW.name,
NEW.lastmodifieddate,
NEW.et4ae5__opened__c,
NEW.ownerid,
NEW.et4ae5__subjectline__c,
NEW.isdeleted,
NEW.et4ae5__contact__c,
NEW.systemmodstamp,
NEW.lastmodifiedbyid,
NEW.et4ae5__datesent__c,
NEW.et4ae5__dateunsubscribed__c,
NEW.createddate,
NEW.createdbyid,
NEW.et4ae5__lead__c,
NEW.et4ae5__tracking_as_of__c,
NEW.et4ae5__numberofuniqueclicks__c,
NEW.et4ae5__senddefinition__c,
NEW.et4ae5__mergeid__c,
NEW.et4ae5__triggeredsenddefinition__c,
NEW.sfid,
NEW.id,
NEW._hc_lastop,
NEW._hc_err,
NEW.isarchived__c)
ON CONFLICT (id)
DO NOTHING;
-- Update SF to reflect the archive
UPDATE salesforce."et4ae5__individualemailresult__c" SET isarchived__c = true, isdeleted = true WHERE id = NEW.id;
END IF;
RETURN NULL;
END;
$BODY$;
ALTER FUNCTION salesforce.archivelogicfunc()
OWNER TO ....;
My understanding is that the NEW.* is only going to contain the rows that caused the trigger to fire in the first place. Therefore if my trigger was fired for a single record, the update statement NEW.id should only update one record on the source table?
Trying to ensure the trigger isn't going to fire again with the update statement causing some recursive loop that I am not expecting.
My concern is:
Record is Updated
Trigger Fires and inserts record into an archive table
Update runs on the source table to update the record for the new.id
This update causes the trigger to run again. The insert would fail due to the on conflict, but the update would then run again, and again etc..
The original trigger is fired AFTER INSERT/UPDATE.
TRIGGER:
CREATE TRIGGER archivelogic_firetrigger
AFTER INSERT OR UPDATE
ON salesforce.et4ae5__individualemailresult__c
FOR EACH ROW
EXECUTE PROCEDURE salesforce.archivelogicfunc();
UPDATE:
I added a WHEN condition to my trigger. It appeared to work on a basic test, but willing to take any other advice if suggested.
CREATE TRIGGER archivelogic_firetrigger
AFTER INSERT OR UPDATE
ON salesforce.et4ae5__individualemailresult__c
FOR EACH ROW
WHEN (pg_trigger_depth() = 0) // <-- Added to prevent recursion
EXECUTE PROCEDURE salesforce.archivelogicfunc();
The easiest would be to make it a before trigger, and to replace the update by
NEW.isarchived__c = true;
NEW. isdeleted = true;
[...]
RETURN NEW;
Otherwise, you can filter the rows before running the trigger: it will be called only when isarchived__c and isdeleted have NOT changed (it may be dangerous though, just imagine someone updating ALL fields)
CREATE TRIGGER archivelogic_firetrigger
AFTER INSERT OR UPDATE
ON salesforce.et4ae5__individualemailresult__c
FOR EACH ROW
WHEN (NEW.isarchived__c IS NOT DISTINCT FROM OLD.isarchived__c
AND NEW.isdeleted IS NOT DISTINCT FROM OLD.isdeleted )
EXECUTE PROCEDURE salesforce.archivelogicfunc();
Background
I have a function that generates detail rows and inserts these into a detail table. I want to automatically ensure that the referenced master row is available before inserting the detail rows.
A BEFORE INSERT trigger does the job, but unfortunately the job is done too well. If a detail row is prevented due to a unique index, the master row will still be inserted, leaving me with a master without children (I don't want that).
I managed to solve this by inserting the master rows inside of a cte and then inserting the detail rows in the actual query. This works, but I'm worried that it's not a safe way of doing it.
INSERT rows from inside of a CTE expression
Here is the code to try this out. The input_cte is just generating static dummy data in the example. This particular example could be built with separate static insert SQLs, but in my real case the input_cte is dynamic.
Is this a safe way to solve this, or is it out of spec and could blow up in the next PG version?
CREATE TABLE master (
id INT NOT NULL GENERATED BY DEFAULT AS IDENTITY,
PRIMARY KEY (id)
);
CREATE TABLE detail (
id INT NOT NULL GENERATED BY DEFAULT AS IDENTITY,
master_id INT,
PRIMARY KEY (id, master_id)
);
ALTER TABLE detail
ADD CONSTRAINT detail_master_id_fkey
FOREIGN KEY (master_id)
REFERENCES master (id);
WITH input_cte AS (
SELECT 1 AS master_id, 1 AS detail_id
UNION SELECT 1, 2
UNION SELECT 2, 1
),
insert_cte AS (
--Ignore conflicts, as the master row could already exist
INSERT INTO master (id)
SELECT DISTINCT master_id
FROM input_cte
ON CONFLICT DO NOTHING
)
INSERT INTO detail (id, master_id)
SELECT detail_id, master_id
FROM input_cte;
SELECT * FROM master;
SELECT * FROM detail;
Edit
Bummer.. I just realised that this method will also insert master rows even if the detail rows would be stopped by my unique index.
I see two options. Which should I choose?
Check exactly what I can insert before trying to insert. I.e. do the same thing as my unique index does.
Go ahead with the above solution or the BEFORE INSERT trigger concept and then clean up unused master rows afterwards with a separate DELETE query.
Edit 2 as a reponse to Haleemur Ali's comment
I agree with Haleemur, but in my case it's a bit more complicated than the small example I created. The unique key on my detail can actually have null values. The index in my detail table (project_sequence) looks like this to enable null values:
CREATE UNIQUE INDEX
project_sequence_unique_combinations ON main.project_sequence
(project_id, controlpoint_type_id, COALESCE(drawing_id, 0), COALESCE(layer_guid, '00000000-0000-0000-0000-000000000000'));
Due to possible NULL values I cannot use these fields in my primary key, so I have a surrogate integer key. I'm calculating these key values in my CTE so they will always be unique. I.e. they can be inserted into the master table (sequence) even if the detail rows gets stopped by the unique index.*
To clarify I've inserted my actual code below. This code works as it should, but it sure would be nice to be able to utilize the new fancy DEFERRED and REFERENCES triggers.
SELECT COALESCE(MAX(id), 0)
INTO _max_sequence_id
FROM main.sequence;
WITH cte AS (
SELECT
d.project_id,
pct.controlpoint_type_id,
d.id as drawing_id,
DENSE_RANK() OVER(ORDER BY d.id, sequence_group_key) + _max_sequence_id + 1 AS new_sequence_id
FROM main.drawing d
CROSS JOIN main.project_controlpoint_type pct
--This left JOIN along with "ps.project_id IS NULL" is my
--current solution, i.e. its "option 1" from above.
LEFT JOIN main.project_sequence ps
ON ps.project_id = d.project_id
AND ps.drawing_id = d.id
AND ps.controlpoint_type_id = pct.controlpoint_type_id
WHERE d.project_id = _project_id
AND pct.project_id = _project_id
AND pct.sequence_level_id = 2
AND ps.project_id IS NULL
),
insert_sequence_cte AS (
INSERT INTO main.sequence
(id, project_id, last_value)
SELECT DISTINCT cte.new_sequence_id, cte.project_id, 0
FROM cte
ON CONFLICT DO NOTHING
)
INSERT INTO main.project_sequence
(project_id, controlpoint_type_id, drawing_id, sequence_id)
SELECT
project_id,
controlpoint_type_id,
drawing_id,
new_sequence_id
FROM cte;
The manual page on WITH queries states that your use case is legitimate and supported:
You can use data-modifying statements (INSERT, UPDATE, or DELETE) in WITH.
and
... data-modifying statements are only allowed in WITH clauses that are attached to the top-level statement. However, normal WITH visibility rules apply, so it is possible to refer to the WITH statement's output from the sub-SELECT.
Further:
If a data-modifying statement in WITH lacks a RETURNING clause, then it forms no temporary table and cannot be referred to in the rest of the query. Such a statement will be executed nonetheless.
If the rule "no master without a detail" is important to your model, you should let the DB enforce it. This will free you from "auto-inserting" master to reduce the potential for error and let you use conventional methods again.
Take a look at CONSTRAINT TRIGGERS. They allow you to just detect and reject violations of your no-master-without-detail rule while leaving the actual INSERTs to application code.
Your use case would need a CONSTRAINT TRIGGER on your master table that is DEFERRABLE INITIALLY DEFERRED. This allows you to INSERT master, then INSERT detail and still be sure that the transaction only commits if all is consistent.
From the manual linked above:
Constraint triggers must be AFTER ROW triggers on plain tables (not foreign tables). They can be fired either at the end of the statement causing the triggering event, or at the end of the containing transaction; in the latter case they are said to be deferred.
You'll need two triggers, one handling INSERT/UPDATE on master and another one handling DELETE/UPDATE on detail:
CREATE CONSTRAINT TRIGGER trigger_assert_master_has_detail
AFTER INSERT OR UPDATE OF id ON master
DEFERRABLE INITIALLY DEFERRED FOR EACH ROW
EXECUTE PROCEDURE assert_master_has_detail();
CREATE CONSTRAINT TRIGGER trigger_assert_no_leftover_master
AFTER DELETE OR UPDATE OF master_id ON detail
DEFERRABLE INITIALLY DEFERRED FOR EACH ROW
EXECUTE PROCEDURE assert_no_leftover_master();
Note that UPDATEs will only fire the trigger if they concern the FK/PK column.
The two trigger functions will then check if there are 1-n details for the master:
CREATE FUNCTION assert_master_has_detail() RETURNS trigger
AS
$$
BEGIN
IF NOT EXISTS (SELECT 1 FROM detail WHERE master_id = NEW.id)
THEN
RAISE EXCEPTION 'no detail for master_id=%', NEW.id;
ELSE
RETURN NEW;
END IF;
END;
$$
LANGUAGE plpgsql;
CREATE FUNCTION assert_no_leftover_master() RETURNS trigger
AS
$$
BEGIN
IF NOT EXISTS (SELECT 1 FROM detail WHERE master_id = OLD.master_id)
AND EXISTS (SELECT 1 FROM master WHERE id = OLD.master_id)
THEN
RAISE EXCEPTION 'last detail for master_id=% removed, but master still exists', OLD.master_id;
ELSE
RETURN NULL;
END IF;
END;
$$
LANGUAGE plpgsql;
Example of a violation:
INSERT INTO master
VALUES (1);
-- ERROR: no detail for master_id=1
-- CONTEXT: PL/pgSQL function assert_master_has_detail() line 5 at RAISE
and a legal scenario:
INSERT INTO master
VALUES (1);
INSERT INTO detail
VALUES (10, 1);
-- trigger fired at end of transaction, finds everything is OK
Here's a complete solution as dbfiddle.
Several months ago I learned from an answer on Stack Overflow how to perform multiple updates at once in MySQL using the following syntax:
INSERT INTO table (id, field, field2) VALUES (1, A, X), (2, B, Y), (3, C, Z)
ON DUPLICATE KEY UPDATE field=VALUES(Col1), field2=VALUES(Col2);
I've now switched over to PostgreSQL and apparently this is not correct. It's referring to all the correct tables so I assume it's a matter of different keywords being used but I'm not sure where in the PostgreSQL documentation this is covered.
To clarify, I want to insert several things and if they already exist to update them.
PostgreSQL since version 9.5 has UPSERT syntax, with ON CONFLICT clause. with the following syntax (similar to MySQL)
INSERT INTO the_table (id, column_1, column_2)
VALUES (1, 'A', 'X'), (2, 'B', 'Y'), (3, 'C', 'Z')
ON CONFLICT (id) DO UPDATE
SET column_1 = excluded.column_1,
column_2 = excluded.column_2;
Searching postgresql's email group archives for "upsert" leads to finding an example of doing what you possibly want to do, in the manual:
Example 38-2. Exceptions with UPDATE/INSERT
This example uses exception handling to perform either UPDATE or INSERT, as appropriate:
CREATE TABLE db (a INT PRIMARY KEY, b TEXT);
CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
LOOP
-- first try to update the key
-- note that "a" must be unique
UPDATE db SET b = data WHERE a = key;
IF found THEN
RETURN;
END IF;
-- not there, so try to insert the key
-- if someone else inserts the same key concurrently,
-- we could get a unique-key failure
BEGIN
INSERT INTO db(a,b) VALUES (key, data);
RETURN;
EXCEPTION WHEN unique_violation THEN
-- do nothing, and loop to try the UPDATE again
END;
END LOOP;
END;
$$
LANGUAGE plpgsql;
SELECT merge_db(1, 'david');
SELECT merge_db(1, 'dennis');
There's possibly an example of how to do this in bulk, using CTEs in 9.1 and above, in the hackers mailing list:
WITH foos AS (SELECT (UNNEST(%foo[])).*)
updated as (UPDATE foo SET foo.a = foos.a ... RETURNING foo.id)
INSERT INTO foo SELECT foos.* FROM foos LEFT JOIN updated USING(id)
WHERE updated.id IS NULL;
See a_horse_with_no_name's answer for a clearer example.
Warning: this is not safe if executed from multiple sessions at the same time (see caveats below).
Another clever way to do an "UPSERT" in postgresql is to do two sequential UPDATE/INSERT statements that are each designed to succeed or have no effect.
UPDATE table SET field='C', field2='Z' WHERE id=3;
INSERT INTO table (id, field, field2)
SELECT 3, 'C', 'Z'
WHERE NOT EXISTS (SELECT 1 FROM table WHERE id=3);
The UPDATE will succeed if a row with "id=3" already exists, otherwise it has no effect.
The INSERT will succeed only if row with "id=3" does not already exist.
You can combine these two into a single string and run them both with a single SQL statement execute from your application. Running them together in a single transaction is highly recommended.
This works very well when run in isolation or on a locked table, but is subject to race conditions that mean it might still fail with duplicate key error if a row is inserted concurrently, or might terminate with no row inserted when a row is deleted concurrently. A SERIALIZABLE transaction on PostgreSQL 9.1 or higher will handle it reliably at the cost of a very high serialization failure rate, meaning you'll have to retry a lot. See why is upsert so complicated, which discusses this case in more detail.
This approach is also subject to lost updates in read committed isolation unless the application checks the affected row counts and verifies that either the insert or the update affected a row.
With PostgreSQL 9.1 this can be achieved using a writeable CTE (common table expression):
WITH new_values (id, field1, field2) as (
values
(1, 'A', 'X'),
(2, 'B', 'Y'),
(3, 'C', 'Z')
),
upsert as
(
update mytable m
set field1 = nv.field1,
field2 = nv.field2
FROM new_values nv
WHERE m.id = nv.id
RETURNING m.*
)
INSERT INTO mytable (id, field1, field2)
SELECT id, field1, field2
FROM new_values
WHERE NOT EXISTS (SELECT 1
FROM upsert up
WHERE up.id = new_values.id)
See these blog entries:
Upserting via Writeable CTE
WAITING FOR 9.1 – WRITABLE CTE
WHY IS UPSERT SO COMPLICATED?
Note that this solution does not prevent a unique key violation but it is not vulnerable to lost updates.
See the follow up by Craig Ringer on dba.stackexchange.com
In PostgreSQL 9.5 and newer you can use INSERT ... ON CONFLICT UPDATE.
See the documentation.
A MySQL INSERT ... ON DUPLICATE KEY UPDATE can be directly rephrased to a ON CONFLICT UPDATE. Neither is SQL-standard syntax, they're both database-specific extensions. There are good reasons MERGE wasn't used for this, a new syntax wasn't created just for fun. (MySQL's syntax also has issues that mean it wasn't adopted directly).
e.g. given setup:
CREATE TABLE tablename (a integer primary key, b integer, c integer);
INSERT INTO tablename (a, b, c) values (1, 2, 3);
the MySQL query:
INSERT INTO tablename (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
becomes:
INSERT INTO tablename (a, b, c) values (1, 2, 10)
ON CONFLICT (a) DO UPDATE SET c = tablename.c + 1;
Differences:
You must specify the column name (or unique constraint name) to use for the uniqueness check. That's the ON CONFLICT (columnname) DO
The keyword SET must be used, as if this was a normal UPDATE statement
It has some nice features too:
You can have a WHERE clause on your UPDATE (letting you effectively turn ON CONFLICT UPDATE into ON CONFLICT IGNORE for certain values)
The proposed-for-insertion values are available as the row-variable EXCLUDED, which has the same structure as the target table. You can get the original values in the table by using the table name. So in this case EXCLUDED.c will be 10 (because that's what we tried to insert) and "table".c will be 3 because that's the current value in the table. You can use either or both in the SET expressions and WHERE clause.
For background on upsert see How to UPSERT (MERGE, INSERT ... ON DUPLICATE UPDATE) in PostgreSQL?
I was looking for the same thing when I came here, but the lack of a generic "upsert" function botherd me a bit so I thought you could just pass the update and insert sql as arguments on that function form the manual
that would look like this:
CREATE FUNCTION upsert (sql_update TEXT, sql_insert TEXT)
RETURNS VOID
LANGUAGE plpgsql
AS $$
BEGIN
LOOP
-- first try to update
EXECUTE sql_update;
-- check if the row is found
IF FOUND THEN
RETURN;
END IF;
-- not found so insert the row
BEGIN
EXECUTE sql_insert;
RETURN;
EXCEPTION WHEN unique_violation THEN
-- do nothing and loop
END;
END LOOP;
END;
$$;
and perhaps to do what you initially wanted to do, batch "upsert", you could use Tcl to split the sql_update and loop the individual updates, the preformance hit will be very small see http://archives.postgresql.org/pgsql-performance/2006-04/msg00557.php
the highest cost is executing the query from your code, on the database side the execution cost is much smaller
There is no simple command to do it.
The most correct approach is to use function, like the one from docs.
Another solution (although not that safe) is to do update with returning, check which rows were updates, and insert the rest of them
Something along the lines of:
update table
set column = x.column
from (values (1,'aa'),(2,'bb'),(3,'cc')) as x (id, column)
where table.id = x.id
returning id;
assuming id:2 was returned:
insert into table (id, column) values (1, 'aa'), (3, 'cc');
Of course it will bail out sooner or later (in concurrent environment), as there is clear race condition in here, but usually it will work.
Here's a longer and more comprehensive article on the topic.
I use this function merge
CREATE OR REPLACE FUNCTION merge_tabla(key INT, data TEXT)
RETURNS void AS
$BODY$
BEGIN
IF EXISTS(SELECT a FROM tabla WHERE a = key)
THEN
UPDATE tabla SET b = data WHERE a = key;
RETURN;
ELSE
INSERT INTO tabla(a,b) VALUES (key, data);
RETURN;
END IF;
END;
$BODY$
LANGUAGE plpgsql
Personally, I've set up a "rule" attached to the insert statement. Say you had a "dns" table that recorded dns hits per customer on a per-time basis:
CREATE TABLE dns (
"time" timestamp without time zone NOT NULL,
customer_id integer NOT NULL,
hits integer
);
You wanted to be able to re-insert rows with updated values, or create them if they didn't exist already. Keyed on the customer_id and the time. Something like this:
CREATE RULE replace_dns AS
ON INSERT TO dns
WHERE (EXISTS (SELECT 1 FROM dns WHERE ((dns."time" = new."time")
AND (dns.customer_id = new.customer_id))))
DO INSTEAD UPDATE dns
SET hits = new.hits
WHERE ((dns."time" = new."time") AND (dns.customer_id = new.customer_id));
Update: This has the potential to fail if simultaneous inserts are happening, as it will generate unique_violation exceptions. However, the non-terminated transaction will continue and succeed, and you just need to repeat the terminated transaction.
However, if there are tons of inserts happening all the time, you will want to put a table lock around the insert statements: SHARE ROW EXCLUSIVE locking will prevent any operations that could insert, delete or update rows in your target table. However, updates that do not update the unique key are safe, so if you no operation will do this, use advisory locks instead.
Also, the COPY command does not use RULES, so if you're inserting with COPY, you'll need to use triggers instead.
Similar to most-liked answer, but works slightly faster:
WITH upsert AS (UPDATE spider_count SET tally=1 WHERE date='today' RETURNING *)
INSERT INTO spider_count (spider, tally) SELECT 'Googlebot', 1 WHERE NOT EXISTS (SELECT * FROM upsert)
(source: http://www.the-art-of-web.com/sql/upsert/)
I custom "upsert" function above, if you want to INSERT AND REPLACE :
`
CREATE OR REPLACE FUNCTION upsert(sql_insert text, sql_update text)
RETURNS void AS
$BODY$
BEGIN
-- first try to insert and after to update. Note : insert has pk and update not...
EXECUTE sql_insert;
RETURN;
EXCEPTION WHEN unique_violation THEN
EXECUTE sql_update;
IF FOUND THEN
RETURN;
END IF;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION upsert(text, text)
OWNER TO postgres;`
And after to execute, do something like this :
SELECT upsert($$INSERT INTO ...$$,$$UPDATE... $$)
Is important to put double dollar-comma to avoid compiler errors
check the speed...
According the PostgreSQL documentation of the INSERT statement, handling the ON DUPLICATE KEY case is not supported. That part of the syntax is a proprietary MySQL extension.
I have the same issue for managing account settings as name value pairs.
The design criteria is that different clients could have different settings sets.
My solution, similar to JWP is to bulk erase and replace, generating the merge record within your application.
This is pretty bulletproof, platform independent and since there are never more than about 20 settings per client, this is only 3 fairly low load db calls - probably the fastest method.
The alternative of updating individual rows - checking for exceptions then inserting - or some combination of is hideous code, slow and often breaks because (as mentioned above) non standard SQL exception handling changing from db to db - or even release to release.
#This is pseudo-code - within the application:
BEGIN TRANSACTION - get transaction lock
SELECT all current name value pairs where id = $id into a hash record
create a merge record from the current and update record
(set intersection where shared keys in new win, and empty values in new are deleted).
DELETE all name value pairs where id = $id
COPY/INSERT merged records
END TRANSACTION
CREATE OR REPLACE FUNCTION save_user(_id integer, _name character varying)
RETURNS boolean AS
$BODY$
BEGIN
UPDATE users SET name = _name WHERE id = _id;
IF FOUND THEN
RETURN true;
END IF;
BEGIN
INSERT INTO users (id, name) VALUES (_id, _name);
EXCEPTION WHEN OTHERS THEN
UPDATE users SET name = _name WHERE id = _id;
END;
RETURN TRUE;
END;
$BODY$
LANGUAGE plpgsql VOLATILE STRICT
For merging small sets, using the above function is fine. However, if you are merging large amounts of data, I'd suggest looking into http://mbk.projects.postgresql.org
The current best practice that I'm aware of is:
COPY new/updated data into temp table (sure, or you can do INSERT if the cost is ok)
Acquire Lock [optional] (advisory is preferable to table locks, IMO)
Merge. (the fun part)
UPDATE will return the number of modified rows. If you use JDBC (Java), you can then check this value against 0 and, if no rows have been affected, fire INSERT instead. If you use some other programming language, maybe the number of the modified rows still can be obtained, check documentation.
This may not be as elegant but you have much simpler SQL that is more trivial to use from the calling code. Differently, if you write the ten line script in PL/PSQL, you probably should have a unit test of one or another kind just for it alone.
Edit: This does not work as expected. Unlike the accepted answer, this produces unique key violations when two processes repeatedly call upsert_foo concurrently.
Eureka! I figured out a way to do it in one query: use UPDATE ... RETURNING to test if any rows were affected:
CREATE TABLE foo (k INT PRIMARY KEY, v TEXT);
CREATE FUNCTION update_foo(k INT, v TEXT)
RETURNS SETOF INT AS $$
UPDATE foo SET v = $2 WHERE k = $1 RETURNING $1
$$ LANGUAGE sql;
CREATE FUNCTION upsert_foo(k INT, v TEXT)
RETURNS VOID AS $$
INSERT INTO foo
SELECT $1, $2
WHERE NOT EXISTS (SELECT update_foo($1, $2))
$$ LANGUAGE sql;
The UPDATE has to be done in a separate procedure because, unfortunately, this is a syntax error:
... WHERE NOT EXISTS (UPDATE ...)
Now it works as desired:
SELECT upsert_foo(1, 'hi');
SELECT upsert_foo(1, 'bye');
SELECT upsert_foo(3, 'hi');
SELECT upsert_foo(3, 'bye');
PostgreSQL >= v15
Big news on this topic as in PostgreSQL v15, it is possible to use MERGE command. In fact, this long awaited feature was listed the first of the improvements of the v15 release.
This is similar to INSERT ... ON CONFLICT but more batch-oriented. It has a powerful WHEN MATCHED vs WHEN NOT MATCHED structure that gives the ability to INSERT, UPDATE or DELETE on such conditions.
It not only eases bulk changes, but it even adds more control that tradition UPSERT and INSERT ... ON CONFLICT
Take a look at this very complete sample from official page:
MERGE INTO wines w
USING wine_stock_changes s
ON s.winename = w.winename
WHEN NOT MATCHED AND s.stock_delta > 0 THEN
INSERT VALUES(s.winename, s.stock_delta)
WHEN MATCHED AND w.stock + s.stock_delta > 0 THEN
UPDATE SET stock = w.stock + s.stock_delta
WHEN MATCHED THEN
DELETE;
PostgreSQL v9, v10, v11, v12, v13, v14
If version is under v15 and over v9.5 , probably best choice is to use UPSERT syntax, with ON CONFLICT clause
Here is the example how to do upsert with params and without special sql constructions
if you have special condition (sometimes you can't use 'on conflict' because you can't create constraint)
WITH upd AS
(
update view_layer set metadata=:metadata where layer_id = :layer_id and view_id = :view_id returning id
)
insert into view_layer (layer_id, view_id, metadata)
(select :layer_id layer_id, :view_id view_id, :metadata metadata FROM view_layer l
where NOT EXISTS(select id FROM upd WHERE id IS NOT NULL) limit 1)
returning id
maybe it will be helpful