I was wondering if it is possible to add an auto-increment integer field on the fly, i.e. without defining it in a CREATE TABLE statement?
For example, I have a statement:
SELECT 1 AS id, t.type FROM t;
and I am can I change this to
SELECT some_nextval_magic AS id, t.type FROM t;
I need to create the auto-increment field on the fly in the some_nextval_magic part because the result relation is a temporary one during the construction of a bigger SQL statement. And the value of id field is not really important as long as it is unique.
I search around here, and the answers to related questions (e.g. PostgreSQL Autoincrement) mostly involving specifying SERIAL or using nextval in CREATE TABLE. But I don't necessarily want to use CREATE TABLE or VIEW (unless I have to). There are also some discussions of generate_series(), but I am not sure whether it applies here.
-- Update --
My motivation is illustrated in this GIS.SE answer regarding the PostGIS extension. The original query was:
CREATE VIEW buffer40units AS
SELECT
g.path[1] as gid,
g.geom::geometry(Polygon, 31492) as geom
FROM
(SELECT
(ST_Dump(ST_UNION(ST_Buffer(geom, 40)))).*
FROM point
) as g;
where g.path[1] as gid is an id field "required for visualization in QGIS". I believe the only requirement is that it is integer and unique across the table. I encountered some errors when running the above query when the g.path[] array is empty.
While trying to fix the array in the above query, this thought came to me:
Since the gid value does not matter anyways, is there an auto-increment function that can be used here instead?
If you wish to have an id field that assigns a unique integer to each row in the output, then use the row_number() window function:
select
row_number() over () as id,
t.type from t;
The generated id will only be unique within each execution of the query. Multiple executions will not generate new unique values for id.
Related
I have a question I know this was posted many times but I didn't find an answer to my problem. The problem is that I have a table and a column "id" I want it to be unique number just as normal. This type of column is serial and the next value after each insert is coming from a sequence so everything seems to be all right but it still sometimes shows this error. I don't know why. In the documentation, it says the sequence is foolproof and always works. If I add a UNIQUE constraint to that column will it help? I worked before many times on Postres but this error is showing for me for the first time. I did everything as normal and I never had this problem before. Can you help me to find the answer that can be used in the future for all tables that will be created? Let's say we have something easy like this:
CREATE TABLE comments
(
id serial NOT NULL,
some_column text NOT NULL,
CONSTRAINT id_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);
ALTER TABLE interesting.comments OWNER TO postgres;
If i add:
ALTER TABLE comments ADD CONSTRAINT id_id_key UNIQUE(id)
Will if be enough or is there some other thing that should be done?
This article explains that your sequence might be out of sync and that you have to manually bring it back in sync.
An excerpt from the article in case the URL changes:
If you get this message when trying to insert data into a PostgreSQL
database:
ERROR: duplicate key violates unique constraint
That likely means that the primary key sequence in the table you're
working with has somehow become out of sync, likely because of a mass
import process (or something along those lines). Call it a "bug by
design", but it seems that you have to manually reset the a primary
key index after restoring from a dump file. At any rate, to see if
your values are out of sync, run these two commands:
SELECT MAX(the_primary_key) FROM the_table;
SELECT nextval('the_primary_key_sequence');
If the first value is higher than the second value, your sequence is
out of sync. Back up your PG database (just in case), then run this command:
SELECT setval('the_primary_key_sequence', (SELECT MAX(the_primary_key) FROM the_table)+1);
That will set the sequence to the next available value that's higher
than any existing primary key in the sequence.
Intro
I also encountered this problem and the solution proposed by #adamo was basically the right solution. However, I had to invest a lot of time in the details, which is why I am now writing a new answer in order to save this time for others.
Case
My case was as follows: There was a table that was filled with data using an app. Now a new entry had to be inserted manually via SQL. After that the sequence was out of sync and no more records could be inserted via the app.
Solution
As mentioned in the answer from #adamo, the sequence must be synchronized manually. For this purpose the name of the sequence is needed. For Postgres, the name of the sequence can be determined with the command PG_GET_SERIAL_SEQUENCE. Most examples use lower case table names. In my case the tables were created by an ORM middleware (like Hibernate or Entity Framework Core etc.) and their names all started with a capital letter.
In an e-mail from 2004 (link) I got the right hint.
(Let's assume for all examples, that Foo is the table's name and Foo_id the related column.)
Command to get the sequence name:
SELECT PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id');
So, the table name must be in double quotes, surrounded by single quotes.
1. Validate, that the sequence is out-of-sync
SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id')) AS "Current Value", MAX("Foo_id") AS "Max Value" FROM "Foo";
When the Current Value is less than Max Value, your sequence is out-of-sync.
2. Correction
SELECT SETVAL((SELECT PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id')), (SELECT (MAX("Foo_id") + 1) FROM "Foo"), FALSE);
Replace the table_name to your actual name of the table.
Gives the current last id for the table. Note it that for next step.
SELECT MAX(id) FROM table_name;
Get the next id sequence according to postgresql. Make sure this id is higher than the current max id we get from step 1
SELECT nextVal('"table_name_id_seq"');
if it's not higher than then use this step 3 to update the next sequence.
SELECT setval('"table_name_id_seq"', (SELECT MAX(id) FROM table_name)+1);
The primary key is already protecting you from inserting duplicate values, as you're experiencing when you get that error. Adding another unique constraint isn't necessary to do that.
The "duplicate key" error is telling you that the work was not done because it would produce a duplicate key, not that it discovered a duplicate key already commited to the table.
For future searchs, use ON CONFLICT DO NOTHING.
Referrence - https://www.calazan.com/how-to-reset-the-primary-key-sequence-in-postgresql-with-django/
I had the same problem try this:
python manage.py sqlsequencereset table_name
Eg:
python manage.py sqlsequencereset auth
you need to run this in production settings(if you have)
and you need Postgres installed to run this on the server
From http://www.postgresql.org/docs/current/interactive/datatype.html
Note: Prior to PostgreSQL 7.3, serial implied UNIQUE. This is no longer automatic. If you wish a serial column to be in a unique constraint or a primary key, it must now be specified, same as with any other data type.
In my case carate table script is:
CREATE TABLE public."Survey_symptom_binds"
(
id integer NOT NULL DEFAULT nextval('"Survey_symptom_binds_id_seq"'::regclass),
survey_id integer,
"order" smallint,
symptom_id integer,
CONSTRAINT "Survey_symptom_binds_pkey" PRIMARY KEY (id)
)
SO:
SELECT nextval('"Survey_symptom_binds_id_seq"'::regclass),
MAX(id)
FROM public."Survey_symptom_binds";
SELECT nextval('"Survey_symptom_binds_id_seq"'::regclass) less than MAX(id) !!!
Try to fix the proble:
SELECT setval('"Survey_symptom_binds_id_seq"', (SELECT MAX(id) FROM public."Survey_symptom_binds")+1);
Good Luck every one!
I had the same problem. It was because of the type of my relations. I had a table property which related to both states and cities. So, at first I had a relation from property to states as OneToOne, and the same for cities. And I had the same error "duplicate key violates unique constraint". That means that: I can only have one property related to one state and city. But that doesnt make sense, because a city can have multiple properties. So the problem is the relation. The relation should be ManyToOne. Many properties to One city
Table name started with a capital letter if tables were created by an ORM middleware (like Hibernate or Entity Framework Core etc.)
SELECT setval('"Table_name_Id_seq"', (SELECT MAX("Id") FROM "Table_name") + 1)
WHERE
NOT EXISTS (
SELECT *
FROM (SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('"Table_name"', 'Id')) AS seq, MAX("Id") AS max_id
FROM "Table_name") AS seq_table
WHERE seq > max_id
)
try that CLI
it's just a suggestion to enhance the adamo code (thanks a lot adamo)
SELECT setval('tableName_columnName_seq', (SELECT MAX(columnName) FROM tableName));
For programatically solution at Django. Based on Paolo Melchiorre's answer, I wrote a chunk as a function to be called before any .save()
from django.db import connection
def setSqlCursor(db_table):
sql = """SELECT pg_catalog.setval(pg_get_serial_sequence('"""+db_table+"""', 'id'), MAX(id)) FROM """+db_table+""";"""
with connection.cursor() as cursor:
cursor.execute(sql)
I have similar problem but I solved it by removing all the foreign key in my Postgresql
I have a view as below in which I union several tables and I'm thinking it might be a good idea to have a unique row number for each row in the result set. The prescient reason is I have an admin tool which doesn't know I'm using a view rather than an ordinary table, and which expects a unique id to be present, but I'm now speculating it might be worth doing more generally (i.e. it may make sense to do this in certain theoretical terms - discussion on this would be welcome). Wondering how to do this in postgresql.
CREATE VIEW subscriptions AS (
SELECT subscriber_id, course, end_at
FROM subscriptions_individual_stripe
UNION ALL SELECT subscriber_id, course, end_at
FROM subscriptions_individual_bank_transfer
ORDER BY end_at DESC);
Discussion
The reason these are separate tables is of course that they are actually different entities, and yet I also need to be able to contemplate them in a combined way, hence the VIEW. This is my way of avoiding so-called 'polymorphic relationships' in certain popular web frameworks.
I have a tool that expects an id and while my first thought was that views don't need a unique key, on the other hand, maybe they do...?
Reason being two records could exist in one of the UNIONed tables which were only unique by virtue of the primary key. If one does not include the primary key, the union should remove one of those, so a record would be lost. Should we also take that into account, i.e. select the primary key (here an integer id) for each of the UNIONed tables, but, "convert it" to some other unique id, so the view has its own unique integer primary key? Of course this won't be usable in terms of referencing anything in the original UNIONed tables, but I'm OK with that (The view is a terminal point of my analysis, I don't intend to do anything further with it, and of course it is not writable).
Update
I'm accepting S-Man's answer below because it is a solution to the question I asked, however, as pointed out, the row_number() must not be treated as if it was a real identifier because it will not be.
So as an important aside, I'm left wondering what row_number() is really intended for then. Perhaps it's (mainly? occasionally?) useful where you want to output some query when you plan to export the data somewhere else (i.e. seems almost spreadsheet-ish), and you abandon any sense of it being integrated with the rest of your database?
Table inheritance may be better as Abelisto has pointed out in the comments.
You can add a row count to the UNION using the row_number() window function:
demo:db<>fiddle
CREATE VIEW v_myview AS
SELECT
row_number() OVER (ORDER BY ...) AS id,
*
FROM (
SELECT ...
UNION
SELECT ...
) AS foo;
The main problem with this is: You should never deal with this id as an real identifier because the data of the table can change. So it could be that one table today generates a few records more than yesterday. So, the generated row numbers wouldn't match to the same record as before.
Edit: Removed the md5 solution I added before because of some problems with uniqueness on same data.
We're in process of converting over from SQL Server to Postgres. I have a scenario that I am trying to accommodate. It involves inserting records from one table into another, WITHOUT listing out all of the columns. I realize this is not recommended practice, but let's set that aside for now.
drop table if exists pk_test_table;
create table public.pk_test_table
(
recordid SERIAL PRIMARY KEY NOT NULL,
name text
);
--example 1: works and will insert a record with an id of 1
insert into pk_test_table values(default,'puppies');
--example 2: fails
insert into pk_test_table
select first_name from person_test;
Error I receive in the second example:
column "recordid" is of type integer but expression is of type
character varying Hint: You will need to rewrite or cast the
expression.
The default keyword will tell the database to grab the next value.
Is there any way to utilize this keyword in the second example? Or some way to tell the database to ignore auto-incremented columns and just them be populated like normal?
I would prefer to not use a subquery to grab the next "id".
This functionality works in SQL Server and hence the question.
Thanks in advance for your help!
If you can't list column names, you should instead use the DEFAULT keyword, as you've done in the simple insert example. This won't work with a in insert into ... select ....
For that, you need to invoke nextval. A subquery is not required, just:
insert into pk_test_table
select nextval('pk_test_table_id_seq'), first_name from person_test;
You do need to know the sequence name. You could get that from information_schema based on the table name and inferring its primary key, using a function that takes just the table name as an argument. It'd be ugly, but it'd work. I don't think there's any way around needing to know the table name.
You're inserting value into the first column, but you need to add a value in the second position.
Therefore you can use INSERT INTO table(field) VALUES(value) syntax.
Since you need to fetch values from another table, you have to remove VALUES and put the subquery there.
insert into pk_test_table(name)
select first_name from person_test;
I hope it helps
I do it this way via a separate function- though I think I'm getting around the issue via the table level having the DEFAULT settings on a per field basis.
create table public.pk_test_table
(
recordid integer NOT NULL DEFAULT nextval('pk_test_table_id_seq'),
name text,
field3 integer NOT NULL DEFAULT 64,
null_field_if_not_set integer,
CONSTRAINT pk_test_table_pkey PRIMARY KEY ("recordid")
);
With function:
CREATE OR REPLACE FUNCTION func_pk_test_table() RETURNS void AS
$BODY$
INSERT INTO pk_test_table (name)
SELECT first_name FROM person_test;
$BODY$
LANGUAGE sql VOLATILE;
Then just execute the function via a SELECT FROM func_pk_test_table();
Notice it hasn't had to specify all the fields- as long as constraints allow it.
Lets say that I have two tables.
The first is: table lists, with list_id SERIAL, list_name TEXT
The second table is, trivially, a table which says if the list is public: list_id INT, is_public INT
Obviously a bit of a contrived case, but I am planning out some tables and this seems to be an issue. If I insert a new list_name into table lists, then it'll give me a new serial number...but now I will need to use that serial number in the second table. Obviously in this case, you could simply add is_public to the first table, but in the case of a linking list where you have a compound key, you'll need to know the serial value that was returned.
How do people usually handle this? Do they get the return type from the insert using whatever system they're interacting with the database with?
One approach to this sort of thing is:
INSERT...
SELECT lastval()
INSERT...
INSERT into the first table, use lastval() to get the "value most recently obtained with nextval for any sequence" (in the current session), and then use that value to build your next INSERT.
There's also INSERT ... RETURNING:
The optional RETURNING clause causes INSERT to compute and return value(s) based on each row actually inserted. This is primarily useful for obtaining values that were supplied by defaults, such as a serial sequence number.
Using INSERT ... RETURNING id basically combines the first two steps above into one so you'd do:
INSERT ... RETURNING id
INSERT ...
where the second INSERT would use the id returned from the first INSERT.
I have a question I know this was posted many times but I didn't find an answer to my problem. The problem is that I have a table and a column "id" I want it to be unique number just as normal. This type of column is serial and the next value after each insert is coming from a sequence so everything seems to be all right but it still sometimes shows this error. I don't know why. In the documentation, it says the sequence is foolproof and always works. If I add a UNIQUE constraint to that column will it help? I worked before many times on Postres but this error is showing for me for the first time. I did everything as normal and I never had this problem before. Can you help me to find the answer that can be used in the future for all tables that will be created? Let's say we have something easy like this:
CREATE TABLE comments
(
id serial NOT NULL,
some_column text NOT NULL,
CONSTRAINT id_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);
ALTER TABLE interesting.comments OWNER TO postgres;
If i add:
ALTER TABLE comments ADD CONSTRAINT id_id_key UNIQUE(id)
Will if be enough or is there some other thing that should be done?
This article explains that your sequence might be out of sync and that you have to manually bring it back in sync.
An excerpt from the article in case the URL changes:
If you get this message when trying to insert data into a PostgreSQL
database:
ERROR: duplicate key violates unique constraint
That likely means that the primary key sequence in the table you're
working with has somehow become out of sync, likely because of a mass
import process (or something along those lines). Call it a "bug by
design", but it seems that you have to manually reset the a primary
key index after restoring from a dump file. At any rate, to see if
your values are out of sync, run these two commands:
SELECT MAX(the_primary_key) FROM the_table;
SELECT nextval('the_primary_key_sequence');
If the first value is higher than the second value, your sequence is
out of sync. Back up your PG database (just in case), then run this command:
SELECT setval('the_primary_key_sequence', (SELECT MAX(the_primary_key) FROM the_table)+1);
That will set the sequence to the next available value that's higher
than any existing primary key in the sequence.
Intro
I also encountered this problem and the solution proposed by #adamo was basically the right solution. However, I had to invest a lot of time in the details, which is why I am now writing a new answer in order to save this time for others.
Case
My case was as follows: There was a table that was filled with data using an app. Now a new entry had to be inserted manually via SQL. After that the sequence was out of sync and no more records could be inserted via the app.
Solution
As mentioned in the answer from #adamo, the sequence must be synchronized manually. For this purpose the name of the sequence is needed. For Postgres, the name of the sequence can be determined with the command PG_GET_SERIAL_SEQUENCE. Most examples use lower case table names. In my case the tables were created by an ORM middleware (like Hibernate or Entity Framework Core etc.) and their names all started with a capital letter.
In an e-mail from 2004 (link) I got the right hint.
(Let's assume for all examples, that Foo is the table's name and Foo_id the related column.)
Command to get the sequence name:
SELECT PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id');
So, the table name must be in double quotes, surrounded by single quotes.
1. Validate, that the sequence is out-of-sync
SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id')) AS "Current Value", MAX("Foo_id") AS "Max Value" FROM "Foo";
When the Current Value is less than Max Value, your sequence is out-of-sync.
2. Correction
SELECT SETVAL((SELECT PG_GET_SERIAL_SEQUENCE('"Foo"', 'Foo_id')), (SELECT (MAX("Foo_id") + 1) FROM "Foo"), FALSE);
Replace the table_name to your actual name of the table.
Gives the current last id for the table. Note it that for next step.
SELECT MAX(id) FROM table_name;
Get the next id sequence according to postgresql. Make sure this id is higher than the current max id we get from step 1
SELECT nextVal('"table_name_id_seq"');
if it's not higher than then use this step 3 to update the next sequence.
SELECT setval('"table_name_id_seq"', (SELECT MAX(id) FROM table_name)+1);
The primary key is already protecting you from inserting duplicate values, as you're experiencing when you get that error. Adding another unique constraint isn't necessary to do that.
The "duplicate key" error is telling you that the work was not done because it would produce a duplicate key, not that it discovered a duplicate key already commited to the table.
For future searchs, use ON CONFLICT DO NOTHING.
Referrence - https://www.calazan.com/how-to-reset-the-primary-key-sequence-in-postgresql-with-django/
I had the same problem try this:
python manage.py sqlsequencereset table_name
Eg:
python manage.py sqlsequencereset auth
you need to run this in production settings(if you have)
and you need Postgres installed to run this on the server
From http://www.postgresql.org/docs/current/interactive/datatype.html
Note: Prior to PostgreSQL 7.3, serial implied UNIQUE. This is no longer automatic. If you wish a serial column to be in a unique constraint or a primary key, it must now be specified, same as with any other data type.
In my case carate table script is:
CREATE TABLE public."Survey_symptom_binds"
(
id integer NOT NULL DEFAULT nextval('"Survey_symptom_binds_id_seq"'::regclass),
survey_id integer,
"order" smallint,
symptom_id integer,
CONSTRAINT "Survey_symptom_binds_pkey" PRIMARY KEY (id)
)
SO:
SELECT nextval('"Survey_symptom_binds_id_seq"'::regclass),
MAX(id)
FROM public."Survey_symptom_binds";
SELECT nextval('"Survey_symptom_binds_id_seq"'::regclass) less than MAX(id) !!!
Try to fix the proble:
SELECT setval('"Survey_symptom_binds_id_seq"', (SELECT MAX(id) FROM public."Survey_symptom_binds")+1);
Good Luck every one!
I had the same problem. It was because of the type of my relations. I had a table property which related to both states and cities. So, at first I had a relation from property to states as OneToOne, and the same for cities. And I had the same error "duplicate key violates unique constraint". That means that: I can only have one property related to one state and city. But that doesnt make sense, because a city can have multiple properties. So the problem is the relation. The relation should be ManyToOne. Many properties to One city
Table name started with a capital letter if tables were created by an ORM middleware (like Hibernate or Entity Framework Core etc.)
SELECT setval('"Table_name_Id_seq"', (SELECT MAX("Id") FROM "Table_name") + 1)
WHERE
NOT EXISTS (
SELECT *
FROM (SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('"Table_name"', 'Id')) AS seq, MAX("Id") AS max_id
FROM "Table_name") AS seq_table
WHERE seq > max_id
)
try that CLI
it's just a suggestion to enhance the adamo code (thanks a lot adamo)
SELECT setval('tableName_columnName_seq', (SELECT MAX(columnName) FROM tableName));
For programatically solution at Django. Based on Paolo Melchiorre's answer, I wrote a chunk as a function to be called before any .save()
from django.db import connection
def setSqlCursor(db_table):
sql = """SELECT pg_catalog.setval(pg_get_serial_sequence('"""+db_table+"""', 'id'), MAX(id)) FROM """+db_table+""";"""
with connection.cursor() as cursor:
cursor.execute(sql)
I have similar problem but I solved it by removing all the foreign key in my Postgresql