I am looking for the best practice to define triggers and sequences on temporary tables with PostgreSQL.
When creating a temp table, PostgreSQL automatically creates a temporary schema with the name "pg_temp_nnn" (alias: "pg_temp")
It appears that one can create user functions and objects in this temporary schema.
I wonder if this is really valid SQL for PostgreSQL or just working by accident?
Tested with various PostgreSQL versions from 10 to 14.
Note: Triggers created on temp tables automatically land in the temp schema because the trigger inherits the schema of its table.
Tx!
CREATE TEMP TABLE tt1 (pk INTEGER NOT NULL, name VARCHAR(50));
CREATE SEQUENCE pg_temp.tt1_seq START 1;
CREATE FUNCTION pg_temp.tt1_srl() RETURNS TRIGGER AS
'DECLARE ls BIGINT;
BEGIN
SELECT INTO ls nextval(''pg_temp.tt1_seq'');
IF new.pk ISNULL OR new.pk=0 THEN
new.pk:=ls;
ELSE
IF new.pk>=ls THEN
PERFORM setval(''pg_temp.tt1_seq'',new.pk);
END IF;
END IF;
RETURN new;
END;'
LANGUAGE 'plpgsql';
CREATE TRIGGER tt1_srlt BEFORE INSERT ON tt1 FOR EACH ROW EXECUTE PROCEDURE pg_temp.tt1_srl();
INSERT INTO tt1 (name) VALUES ('aaaa');
SELECT 'Insert #1:', currval('pg_temp.tt1_seq');
INSERT INTO tt1 VALUES (0,'bbbb');
SELECT 'Insert #2:', currval('pg_temp.tt1_seq');
INSERT INTO tt1 VALUES (100,'cccc');
SELECT 'Insert #3:', currval('pg_temp.tt1_seq');
INSERT INTO tt1 (name) VALUES ('dddd');
SELECT 'Insert #4:', currval('pg_temp.tt1_seq');
SELECT * FROM tt1 ORDER BY pk;
Output:
CREATE TABLE
CREATE SEQUENCE
CREATE FUNCTION
CREATE TRIGGER
INSERT 0 1
?column? | currval
------------+---------
Insert #1: | 1
(1 row)
INSERT 0 1
?column? | currval
------------+---------
Insert #2: | 2
(1 row)
INSERT 0 1
?column? | currval
------------+---------
Insert #3: | 100
(1 row)
INSERT 0 1
?column? | currval
------------+---------
Insert #4: | 101
(1 row)
pk | name
-----+------
1 | aaaa
2 | bbbb
100 | cccc
101 | dddd
(4 rows)
Yes, that works and is supported.
Creating objects in schema pg_temp creates temporary objects that will be removed when the session ends. CREATE TEMP TABLE x (...) is the same as CREATE TABLE pg_temp.x (...).
I would like to create check constraint on the HSTORE field that contains data in a following format:
{
1 => 2020-03-01, 2 => 2020-03-07, etc, etc, etc,
}
Where key is always a positive digit and value is a date.
Problem here that I want to extract keys ( by akeys), and then somehow get the biggest key and compare it with number_of_episodes(positive integer).
But it says that I can’t use arrays in check constraint.
Question is -is it possible to extract somehow biggest key from HSTORE as an integer and use it in check constraint afterwards?
Thank you.
alter table archives_seasonmodel
add constraint test
check (max((unnest(akeys(episodes))) <= number_of_episodes ))
This doesn’t work.
This works for me in PostgreSQL 10:
# create table tvseries
(number_of_episodes int,
episodes hstore,
check (number_of_episodes >= all (akeys(episodes)::int[]))
);
CREATE TABLE
# insert into tvseries values (2, '1=>"a", 2=>"b"');
INSERT 0 1
# insert into tvseries values (1, '1=>"a", 2=>"b"');
ERROR: new row for relation "tvseries" violates check constraint "tvseries_check"
DETAIL: Failing row contains (1, "1"=>"a", "2"=>"b").
# insert into tvseries values (2, '1=>"a"');
INSERT 0 1
# select * from tvseries;
number_of_episodes | episodes
--------------------+--------------------
2 | "1"=>"a", "2"=>"b"
2 | "1"=>"a"
(2 rows)
This answer outlines a couple ways you can go about this. The first is to use the intarray extension and it's sort_desc function, but I think the better approach here is to use a custom function.
testdb=# create extension hstore;
CREATE EXTENSION
testdb=# create table tt0(h hstore, max_n bigint);
CREATE TABLE
testdb=# CREATE OR REPLACE FUNCTION array_greatest(anyarray)
RETURNS anyelement LANGUAGE SQL AS $$
SELECT max(x) FROM unnest($1) as x;
$$;
CREATE FUNCTION
testdb=# alter table tt0 add check((array_greatest(akeys(h)::integer[]))<=max_n);
ALTER TABLE
testdb=# insert into tt0 select hstore(ARRAY[['1','asdf'],['3','fdsa']]), 2;
ERROR: new row for relation "tt0" violates check constraint "tt0_check"
DETAIL: Failing row contains ("1"=>"asdf", "3"=>"fdsa", 2).
testdb=# insert into tt0 select hstore(ARRAY[['1','asdf'],['2','fdsa']]), 2;
INSERT 0 1
testdb=# select * from tt0
testdb-# ;
h | max_n
--------------------------+-------
"1"=>"asdf", "2"=>"fdsa" | 2
(1 row)
testdb=# \d tt0
Table "public.tt0"
Column | Type | Collation | Nullable | Default
--------+--------+-----------+----------+---------
h | hstore | | |
max_n | bigint | | |
Check constraints:
"tt0_check" CHECK (array_greatest(akeys(h)::integer[]) <= max_n)
I did some research but can't find the exact answer that I look for. Currently I have a primary key column 'id' which is set to serial but I want to change it to bigserial to map to Long in Java layer. What is the best way to achieve this considering this is a existing table? I think my Postgres version is 10.5. Also I am aware that both serial and bigserial are not a data type.
In Postgres 9.6 or earlier the sequence created by a serial column already returns bigint. You can check this using psql:
drop table if exists my_table;
create table my_table(id serial primary key, str text);
\d my_table
Table "public.my_table"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+--------------------------------------
id | integer | | not null | nextval('my_table_id_seq'::regclass)
str | text | | |
Indexes:
"my_table_pkey" PRIMARY KEY, btree (id)
\d my_table_id_seq
Sequence "public.my_table_id_seq"
Type | Start | Minimum | Maximum | Increment | Cycles? | Cache
--------+-------+---------+---------------------+-----------+---------+-------
bigint | 1 | 1 | 9223372036854775807 | 1 | no | 1
Owned by: public.my_table.id
So you should only alter the type of the serial column:
alter table my_table alter id type bigint;
The behavior has changed in Postgres 10:
Also, sequences created for SERIAL columns now generate positive 32-bit wide values, whereas previous versions generated 64-bit wide values. This has no visible effect if the values are only stored in a column.
Hence in Postgres 10+:
alter sequence my_table_id_seq as bigint;
alter table my_table alter id type bigint;
-- backup table first
CREATE TABLE tablenamebackup as select * from tablename ;
--add new column idx
alter table tablename add column idx bigserial not null;
-- copy id to idx
update tablename set idx = id ;
-- drop id column
alter table tablename drop column id ;
-- rename idx to id
alter table tablename rename column idx to id ;
-- Reset Sequence to max + 1
SELECT setval(pg_get_serial_sequence('tablename', 'id'), coalesce(max(id)+1, 1), false) FROM tablename ;
Assuming I have a parent table with child partitions that are created based on the value of a field.
If the value of that field changes, is there a way to have Postgres automatically move the row into the appropriate partition?
For example:
create table my_table(name text)
partition by list (left(name, 1));
create table my_table_a
partition of my_table
for values in ('a');
create table my_table_b
partition of my_table
for values in ('b');
In this case, if I change the value of name in a row from aaa to bbb, how can I get it to automatically move that row into my_table_b.
When I tried to do that, (i.e. update my_table set name = 'bbb' where name = 'aaa';), I get the following error:
ERROR: new row for relation "my_table_a" violates partition constraint
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=f0e44751d7175fa3394da2c8f85e3ceb3cdbfe63
it doesn't handle updates that cross partition boundaries.
thus you need to create one yourself... here's your set:
t=# insert into my_table select 'abc';
INSERT 0 1
t=# insert into my_table select 'bcd';
INSERT 0 1
t=# select tableoid::regclass,* from my_table;
tableoid | name
------------+------
my_table_a | abc
my_table_b | bcd
(2 rows)
here's rule and fn():
t=# create or replace function puf(_j json,_o text) returns void as $$
begin
raise info '%',': '||left(_j->>'name',1);
execute format('insert into %I select * from json_populate_record(null::my_table, %L)','my_table_'||left(_j->>'name',1), _j);
execute format('delete from %I where name = %L','my_table_'||left(_o,1), _o);
end;
$$language plpgsql;
CREATE FUNCTION
t=# create rule psr AS ON update to my_table do instead select puf(row_to_json(n),OLD.name) from (select NEW.*) n;
CREATE RULE
here's update:
t=# update my_table set name = 'bbb' where name = 'abc';
INFO: : b
puf
-----
(1 row)
UPDATE 0
checking result:
t=# select tableoid::regclass,* from my_table;
tableoid | name
------------+------
my_table_b | bcd
my_table_b | bbb
(2 rows)
once again:
t=# update my_table set name = 'a1' where name = 'bcd';
INFO: : a
puf
-----
(1 row)
UPDATE 0
t=# select tableoid::regclass,* from my_table;
tableoid | name
------------+------
my_table_a | a1
my_table_b | bbb
(2 rows)
Of course using json to pass NEW record looks ugly. And it is ugly indeed. But I did not have time to study the new PARTITION feature of 10, so don't know the elegant way to do this task. Hopefully I could give the generic idea of how you can possible solve the problem and you will produce a better neat code.
update
its probablygood idea to limit such rule to ON update to my_table where left(NEW.name,1) <> left(OLD.name,1) do instead, to release the heavy manipulations need
I'm switching from MySQL to PostgreSQL and I was wondering how can I have an INT column with AUTO INCREMENT. I saw in the PostgreSQL docs a datatype called SERIAL, but I get syntax errors when using it.
Yes, SERIAL is the equivalent function.
CREATE TABLE foo (
id SERIAL,
bar varchar
);
INSERT INTO foo (bar) VALUES ('blah');
INSERT INTO foo (bar) VALUES ('blah');
SELECT * FROM foo;
+----------+
| 1 | blah |
+----------+
| 2 | blah |
+----------+
SERIAL is just a create table time macro around sequences. You can not alter SERIAL onto an existing column.
You can use any other integer data type, such as smallint.
Example :
CREATE SEQUENCE user_id_seq;
CREATE TABLE user (
user_id smallint NOT NULL DEFAULT nextval('user_id_seq')
);
ALTER SEQUENCE user_id_seq OWNED BY user.user_id;
Better to use your own data type, rather than user serial data type.
If you want to add sequence to id in the table which already exist you can use:
CREATE SEQUENCE user_id_seq;
ALTER TABLE user ALTER user_id SET DEFAULT NEXTVAL('user_id_seq');
Starting with Postgres 10, identity columns as defined by the SQL standard are also supported:
create table foo
(
id integer generated always as identity
);
creates an identity column that can't be overridden unless explicitly asked for. The following insert will fail with a column defined as generated always:
insert into foo (id)
values (1);
This can however be overruled:
insert into foo (id) overriding system value
values (1);
When using the option generated by default this is essentially the same behaviour as the existing serial implementation:
create table foo
(
id integer generated by default as identity
);
When a value is supplied manually, the underlying sequence needs to be adjusted manually as well - the same as with a serial column.
An identity column is not a primary key by default (just like a serial column). If it should be one, a primary key constraint needs to be defined manually.
Whilst it looks like sequences are the equivalent to MySQL auto_increment, there are some subtle but important differences:
1. Failed Queries Increment The Sequence/Serial
The serial column gets incremented on failed queries. This leads to fragmentation from failed queries, not just row deletions. For example, run the following queries on your PostgreSQL database:
CREATE TABLE table1 (
uid serial NOT NULL PRIMARY KEY,
col_b integer NOT NULL,
CHECK (col_b>=0)
);
INSERT INTO table1 (col_b) VALUES(1);
INSERT INTO table1 (col_b) VALUES(-1);
INSERT INTO table1 (col_b) VALUES(2);
SELECT * FROM table1;
You should get the following output:
uid | col_b
-----+-------
1 | 1
3 | 2
(2 rows)
Notice how uid goes from 1 to 3 instead of 1 to 2.
This still occurs if you were to manually create your own sequence with:
CREATE SEQUENCE table1_seq;
CREATE TABLE table1 (
col_a smallint NOT NULL DEFAULT nextval('table1_seq'),
col_b integer NOT NULL,
CHECK (col_b>=0)
);
ALTER SEQUENCE table1_seq OWNED BY table1.col_a;
If you wish to test how MySQL is different, run the following on a MySQL database:
CREATE TABLE table1 (
uid int unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
col_b int unsigned NOT NULL
);
INSERT INTO table1 (col_b) VALUES(1);
INSERT INTO table1 (col_b) VALUES(-1);
INSERT INTO table1 (col_b) VALUES(2);
You should get the following with no fragementation:
+-----+-------+
| uid | col_b |
+-----+-------+
| 1 | 1 |
| 2 | 2 |
+-----+-------+
2 rows in set (0.00 sec)
2. Manually Setting the Serial Column Value Can Cause Future Queries to Fail.
This was pointed out by #trev in a previous answer.
To simulate this manually set the uid to 4 which will "clash" later.
INSERT INTO table1 (uid, col_b) VALUES(5, 5);
Table data:
uid | col_b
-----+-------
1 | 1
3 | 2
5 | 5
(3 rows)
Run another insert:
INSERT INTO table1 (col_b) VALUES(6);
Table data:
uid | col_b
-----+-------
1 | 1
3 | 2
5 | 5
4 | 6
Now if you run another insert:
INSERT INTO table1 (col_b) VALUES(7);
It will fail with the following error message:
ERROR: duplicate key value violates unique constraint "table1_pkey"
DETAIL: Key (uid)=(5) already exists.
In contrast, MySQL will handle this gracefully as shown below:
INSERT INTO table1 (uid, col_b) VALUES(4, 4);
Now insert another row without setting uid
INSERT INTO table1 (col_b) VALUES(3);
The query doesn't fail, uid just jumps to 5:
+-----+-------+
| uid | col_b |
+-----+-------+
| 1 | 1 |
| 2 | 2 |
| 4 | 4 |
| 5 | 3 |
+-----+-------+
Testing was performed on MySQL 5.6.33, for Linux (x86_64) and PostgreSQL 9.4.9
Sorry, to rehash an old question, but this was the first Stack Overflow question/answer that popped up on Google.
This post (which came up first on Google) talks about using the more updated syntax for PostgreSQL 10:
https://blog.2ndquadrant.com/postgresql-10-identity-columns/
which happens to be:
CREATE TABLE test_new (
id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
);
Hope that helps :)
You have to be careful not to insert directly into your SERIAL or sequence field, otherwise your write will fail when the sequence reaches the inserted value:
-- Table: "test"
-- DROP TABLE test;
CREATE TABLE test
(
"ID" SERIAL,
"Rank" integer NOT NULL,
"GermanHeadword" "text" [] NOT NULL,
"PartOfSpeech" "text" NOT NULL,
"ExampleSentence" "text" NOT NULL,
"EnglishGloss" "text"[] NOT NULL,
CONSTRAINT "PKey" PRIMARY KEY ("ID", "Rank")
)
WITH (
OIDS=FALSE
);
-- ALTER TABLE test OWNER TO postgres;
INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
VALUES (1, '{"der", "die", "das", "den", "dem", "des"}', 'art', 'Der Mann küsst die Frau und das Kind schaut zu', '{"the", "of the" }');
INSERT INTO test("ID", "Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
VALUES (2, 1, '{"der", "die", "das"}', 'pron', 'Das ist mein Fahrrad', '{"that", "those"}');
INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
VALUES (1, '{"der", "die", "das"}', 'pron', 'Die Frau, die nebenen wohnt, heißt Renate', '{"that", "who"}');
SELECT * from test;
In the context of the asked question and in reply to the comment by #sereja1c, creating SERIAL implicitly creates sequences, so for the above example-
CREATE TABLE foo (id SERIAL,bar varchar);
CREATE TABLE would implicitly create sequence foo_id_seq for serial column foo.id. Hence, SERIAL [4 Bytes] is good for its ease of use unless you need a specific datatype for your id.
Since PostgreSQL 10
CREATE TABLE test_new (
id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
payload text
);
This way will work for sure, I hope it helps:
CREATE TABLE fruits(
id SERIAL PRIMARY KEY,
name VARCHAR NOT NULL
);
INSERT INTO fruits(id,name) VALUES(DEFAULT,'apple');
or
INSERT INTO fruits VALUES(DEFAULT,'apple');
You can check this the details in the next link:
http://www.postgresqltutorial.com/postgresql-serial/
Create Sequence.
CREATE SEQUENCE user_role_id_seq
INCREMENT 1
MINVALUE 1
MAXVALUE 9223372036854775807
START 3
CACHE 1;
ALTER TABLE user_role_id_seq
OWNER TO postgres;
and alter table
ALTER TABLE user_roles ALTER COLUMN user_role_id SET DEFAULT nextval('user_role_id_seq'::regclass);