I used pg_dump to populate a table in new database. After that, I want to be able to insert rows into table using the default autoincrementer of the serial key. Here is what I have in table:
In this table (smtable), a is the key (set as serial).
--data filled using pg dump
a | b
1 2
2 5
Now when I do the following statement:
INSERT INTO smtable VALUES(DEFAULT, 6)
RETURNING a INTO id;
I get the following error:
[error: duplicate key value violates unique constraint "a_pkey"]
detail: 'Key (a)=(1) already exists.
How do I get this statement to insert next_key of the table..
You might set the serial to the greatest number of your current id column to solve the issue. Since serial columns are associated with a sequence, just set it using this:
SELECT setval('smtable_a_seq', max(a)) FROM table;
Related
I have a Postgres 10.6 table with a serial ID column.
When I attempt to insert into it:
INSERT INTO table (col1, col2) VALUES ('foo', 'bar');
excluding the ID column from the column list, I get:
ERROR: duplicate key value violates unique constraint "customer_invoice_pkey"
Detail: Key (id)=(1234) already exists.
Subsequent runs of the query increment the ID in the error message (1235, 1236 etc.)
How can this be happening?
Having a serial column does not prevent you from inserting rows with an explicit value for id. The sequence value is only a default value that is used when id is not specified in the INSERT statement.
So there must have been some “rogue” inserts of that kind. From PostgreSQL v11 on, you can use identity columns (GENERATED ALWAYS AS IDENTITY) to make overriding the sequence value harder.
You could use the setval function to set the sequence to a value higher than the maximum id in the table to work around the problem.
I have a table with existing data. Is there a way to add a primary key without deleting and re-creating the table?
(Updated - Thanks to the people who commented)
Modern Versions of PostgreSQL
Suppose you have a table named test1, to which you want to add an auto-incrementing, primary-key id (surrogate) column. The following command should be sufficient in recent versions of PostgreSQL:
ALTER TABLE test1 ADD COLUMN id SERIAL PRIMARY KEY;
Older Versions of PostgreSQL
In old versions of PostgreSQL (prior to 8.x?) you had to do all the dirty work. The following sequence of commands should do the trick:
ALTER TABLE test1 ADD COLUMN id INTEGER;
CREATE SEQUENCE test_id_seq OWNED BY test1.id;
ALTER TABLE test1 ALTER COLUMN id SET DEFAULT nextval('test_id_seq');
UPDATE test1 SET id = nextval('test_id_seq');
Again, in recent versions of Postgres this is roughly equivalent to the single command above.
ALTER TABLE test1 ADD COLUMN id SERIAL PRIMARY KEY;
This is all you need to:
Add the id column
Populate it with a sequence from 1 to count(*).
Set it as primary key / not null.
Credit is given to #resnyanskiy who gave this answer in a comment.
To use an identity column in v10,
ALTER TABLE test
ADD COLUMN id { int | bigint | smallint}
GENERATED { BY DEFAULT | ALWAYS } AS IDENTITY PRIMARY KEY;
For an explanation of identity columns, see https://blog.2ndquadrant.com/postgresql-10-identity-columns/.
For the difference between GENERATED BY DEFAULT and GENERATED ALWAYS, see https://www.cybertec-postgresql.com/en/sequences-gains-and-pitfalls/.
For altering the sequence, see https://popsql.io/learn-sql/postgresql/how-to-alter-sequence-in-postgresql/.
I landed here because I was looking for something like that too. In my case, I was copying the data from a set of staging tables with many columns into one table while also assigning row ids to the target table. Here is a variant of the above approaches that I used.
I added the serial column at the end of my target table. That way I don't have to have a placeholder for it in the Insert statement. Then a simple select * into the target table auto populated this column. Here are the two SQL statements that I used on PostgreSQL 9.6.4.
ALTER TABLE target ADD COLUMN some_column SERIAL;
INSERT INTO target SELECT * from source;
ALTER TABLE test1 ADD id int8 NOT NULL GENERATED ALWAYS AS IDENTITY;
My table has three rows and i don't want to add any more rows.
However i want to be able to select & update on the table.
What is the best way to block further inserts ?
Assuming you have a primary key named id with the current values 1,2 and 3 you could do something like this:
alter table the_table
add constraint limit_values check (id in (1,2,3));
Now if you try to insert a new row, you either get a primary key violation (because 1,2 and 3 already exist) or you get a check constraint violation when you try to insert a different ID value that does not yet exist.
I am following an PostgreSQL book, and had to import a CSV file into a table census.lu_tracts.
Problem: When performing the INSERT query as shown below, I get the error:
ERROR: duplicate key value violates unique constraint "pk_lu_tracts"
DETAIL: Key (tract_id)=(25001010800) already exists.
How did the key becomes duplicate? SELECT * from lu_tracs shows 0 rows.
CREATE SCHEMA census;
set search_path=census;
CREATE TABLE lu_tracts(tract_id varchar(11), tract_long_id varchar(25)
, tract_name varchar(150)
, CONSTRAINT pk_lu_tracts PRIMARY KEY (tract_id));
INSERT INTO lu_tracts( tract_id, tract_long_id, tract_name)
SELECT geo_id2, geo_id, geo_display
FROM staging.factfinder_import
WHERE geo_id2 ~ '^[0-9]+';
The right answer is DISTINCT ON (geo_id2) which will select only one row per geo_id2 (more in the manual), it should be accompanied by an ORDER BY clause that will specify what row will be choosen.
I am puzzled by a weird Postgres problem I encounter in the trivial database shown below: If I first insert a tag and explicitly specify its ID and then try to insert another tag without passing an ID, then this second insert fails. If I try a third time (again without ID), the insert succeeds.
DROP DATABASE IF EXISTS mydb;
CREATE DATABASE mydb;
\c mydb
DROP SCHEMA public;
CREATE SCHEMA core;
CREATE TABLE core.tag
(
id serial PRIMARY KEY,
title text NOT NULL
);
-- this works: all columns specified explicitly
INSERT INTO core.tag(id, title) VALUES (1, 'known tag');
-- omitting the tag ID fails with
-- ERROR: duplicate key value violates unique constraint "tag_pkey"
-- DETAIL: Key (id)=(1) already exists.
INSERT INTO core.tag(title) VALUES ('unknown tag');
-- this works again ?!?
INSERT INTO core.tag(title) VALUES ('unknown tag');
The issue only seems to occur on a freshly created database and once it does, it does not seem to happen again. I have never come across anything like this - so far, I have just inserted data with or without explicit ID and AFAICS, nothing ever failed like this...
Does anyone have an idea what's going on here ?!?
Environment: PostgreSQL 9.1.3 on Mac OSX 10.7.5
Of course this fails.
What happens?
When you create the table, a sequence is also created that generates the values for the ID column. The sequence starts with 1 but it is only used if you do not specify a value for the ID column.
Now when you run
INSERT INTO core.tag(id, title) VALUES (1, 'known tag');
you bypass Postgres' automatic assigment of the ID value, the sequence "stays" at one.
Now when you run
INSERT INTO core.tag(title) VALUES ('unknown tag');
Postgres takes the next value from the sequence - which is 1. But that alreay exists so the insert fails. After taking the value from the sequence, the next value is 2, so the subsequent insert without specifying an ID value gets the 2 and succeeds.
The solution is to either never include the ID column in your inserts. Or - if you do - request the ID from the sequence:
INSERT INTO core.tag(id, title) VALUES (nextval('tag_id_seq'), 'known tag');
When a serial column is created it is automatically associated with a sequence which is named <table_name>_<column_name>_seq. And that's the name I used in the above statement.
More details about how the serial "data type" works are in the manual: http://www.postgresql.org/docs/current/static/datatype-numeric.html#DATATYPE-SERIAL