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;
Related
I have some tables in PostgreSQL 12.9 that were declared as something like
-- This table is written in old style
create table old_style_table_1 (
id bigserial not null primary key,
...
);
-- This table uses new feature
create table new_style_table_2 (
id bigint generated by default as identity,
...
);
Second table seems to be declared using the identity flag introduced in 10th version.
Time went by, and we have partitioned the old tables, while keeping the original sequences:
CREATE TABLE partitioned_old_style_table_1 (LIKE old_style_table_1 INCLUDING DEFAULTS) PARTITION BY HASH (user_id);
CREATE TABLE partitioned_new_style_table_2 (LIKE new_style_table_2 INCLUDING DEFAULTS) PARTITION BY HASH (user_id);
DDL for their id columns seems to be id bigint default nextval('old_style_table_1_id_seq') not null and id bigint default nextval('new_style_table_2_id_seq') not null.
Everything has worked fine so far. Partitioned tables proved to be a great boon and we decided to retire the old tables by dropping them.
DROP TABLE old_style_table_1, new_style_table_2;
-- [2BP01] ERROR: cannot drop desired object(s) because other objects depend on them
-- Detail: default value for column id of table old_style_table_1 depends on sequence old_style_table_1_id_seq
-- default value for column id of table new_style_table_2 depends on sequence new_style_table_2_id_seq
After some pondering I've found out that sequences may have owners in postgres, so I opted to change them:
ALTER SEQUENCE old_style_table_1_id_seq OWNED BY partitioned_old_style_table_1.id;
DROP TABLE old_style_table_1;
-- Worked out flawlessly
ALTER SEQUENCE new_style_table_2_id_seq OWNED BY partitioned_new_style_table_2.id;
ALTER SEQUENCE new_style_table_2_id_seq OWNED BY NONE;
-- Here's the culprit of the question:
-- [0A000] ERROR: cannot change ownership of identity sequence
So, apparently the fact that this column has pg_attribute.attidentity set to 'd' forbids me from:
• changing the default value of the column:
ALTER TABLE new_style_table_2 ALTER COLUMN id SET DEFAULT 0;
-- [42601] ERROR: column "id" of relation "new_style_table_2" is an identity column
• dropping the default value:
ALTER TABLE new_style_table_2 ALTER COLUMN id DROP DEFAULT;
-- [42601] ERROR: column "id" of relation "new_style_table_2" is an identity column
-- Hint: Use ALTER TABLE ... ALTER COLUMN ... DROP IDENTITY instead.
• dropping the identity, column or the table altogether (new tables already depend on the sequence):
ALTER TABLE new_style_table_2 ALTER COLUMN id DROP IDENTITY IF EXISTS;
-- or
ALTER TABLE new_style_table_2 DROP COLUMN id;
-- or
DROP TABLE new_style_table_2;
-- result in
-- [2BP01] ERROR: cannot drop desired object(s) because other objects depend on them
-- default value for column id of table partitioned_new_style_table_2 depends on sequence new_style_table_2_id_seq
I've looked up the documentation, it provides the way to SET IDENTITY or ADD IDENTITY, but no way to remove it or to change to a throwaway sequence without attempting to drop the existing one.
➥ So, how am I able to remove an identity flag from the column-sequence pair so it won't affect other tables that use this sequence?
UPD: Tried running UPDATE pg_attribute SET attidentity='' WHERE attrelid=16816; on localhost, still receive [2BP01] and [0A000]. :/
Though I managed to execute the DROP DEFAULT value bit, but it seems like a dead end.
I don't think there is a safe and supported way to do that (without catalog modifications). Fortunately, there is nothing special about sequences that would make dropping them a problem. So take a short down time and:
remove the default value that uses the identity sequence
record the current value of the sequence
drop the table
create a new sequence with an appropriate START value
use the new sequence to set new default values
If you want an identity column, you should define it on the partitioned table, not on one of the partitions.
In database dump created with pg_dump, some tables have DEFAULTs in the CREATE TABLE statement, i.e.:
CREATE TABLE test (
f1 integer DEFAULT nextval('test_f1_seq'::regclass) NOT NULL
);
But others have an additional ALTER statement:
ALTER TABLE ONLY test2 ALTER COLUMN f1 SET DEFAULT nextval('test2_f1_seq'::regclass);
What is the reason of this? All sequential fields were created with type SERIAL, but in the dump they look different, and I can't guess any rule for this.
The difference must be that in the first case, the sequence is “owned” by the table column.
You can specify this dependency using the OWNED BY clause when you create a sequence. A sequence that is owned by a column will automatically be dropped when the column is.
If a sequence is implicitly created by using serial, it will be owned by the column.
I am new in PostgreSQL and I am working with this database.
I got a file which I imported, and I am trying to get rows with a certain ID. But the ID is not defined, as you can see it in this picture:
so how do I access this ID? I want to use an SQL command like this:
SELECT * from table_name WHERE ID = 1;
If any order of rows is ok for you, just add a row number according to the current arbitrary sort order:
CREATE SEQUENCE tbl_tbl_id_seq;
ALTER TABLE tbl ADD COLUMN tbl_id integer DEFAULT nextval('tbl_tbl_id_seq');
The new default value is filled in automatically in the process. You might want to run VACUUM FULL ANALYZE tbl to remove bloat and update statistics for the query planner afterwards. And possibly make the column your new PRIMARY KEY ...
To make it a fully fledged serial column:
ALTER SEQUENCE tbl_tbl_id_seq OWNED BY tbl.tbl_id;
See:
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
What you see are just row numbers that pgAdmin displays, they are not really stored in the database.
If you want an artificial numeric primary key for the table, you'll have to create it explicitly.
For example:
CREATE TABLE mydata (
id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
obec text NOT NULL,
datum timestamp with time zone NOT NULL,
...
);
Then to copy the data from a CSV file, you would run
COPY mydata (obec, datum, ...) FROM '/path/to/csvfile' (FORMAT 'csv');
Then the id column is automatically filled.
I am relatively new to postgres (I am a django user - use pgsql via the orm), and I am trying to figure out a way to insert content into a specfic column - but so far, am not having any luck. So, I first have a database dzmodel_uf with two columns: id (which is the PK) and content - both of which are populated (say 50 entries).
Now, I would like to create another table, which references (foreign keys) to id of dzmodel_uf. So, I do the following:
--INITIALIZATION
CREATE TABLE MyNewTable(id integer REFERENCES dzmodel_uf (id));
ALTER TABLE ONLY FullTextSearch ADD CONSTRAINT mynewtable_pkey PRIMARY KEY (id);
which works fine. Now, I create a column on my MyNewTable table like so:
ALTER TABLE MyNewTable ADD COLUMN content_tsv_gin tsvector;
..which also works fine. Finally, I would like to add the content from dzmodel_uf - column content like so:
UPDATE MyNewTable SET content_tsv_gin = to_tsvector('public.wtf', dzmodel_uf(content) )
.. but this FAILS and says that column content does not exist..
In a nutshell, I am not sure how I can reference values from another table.
I hope I understood the question (it is rather fuzzy).There are no rows in the target table, so you have to add them.
You need INSERT, not UPDATE :
INSERT INTO MyNewTable (id,content_tsv_gin)
SELECT dzu.id, to_tsvector( public.wtf, dzu.content )
FROM dzmodel_uf dzu
;
Is there a way to set the PRIMARY KEY in a single "CREATE TABLE AS" statement?
Example - I would like the following to be written in 1 statement rather than 2:
CREATE TABLE "new_table_name" AS SELECT a.uniquekey, a.some_value + b.some_value FROM "table_a" AS a, "table_b" AS b WHERE a.uniquekey=b.uniquekey;
ALTER TABLE "new_table_name" ADD PRIMARY KEY (uniquekey);
Is there a better way of doing this in general (assume there are more than 2 tables, e.g. 10)?
According to the manual: create table and create table as you can either:
create table with primary key first, and use select into later
create table as first, and use add primary key later
But not both create table as with primary key - what you wanted.
If you want to create a new table with the same table structure of another table, you can do this in one statement (both creating a new table and setting the primary key) like this:
CREATE TABLE mytable_clone (
LIKE mytable
INCLUDING defaults
INCLUDING constraints
INCLUDING indexes
);
No, there is no shorter way to create the table and the primary key.
See the command below, it will create a new table with all the constraints and with no data. Worked in postgres 9.5
CREATE TABLE IF NOT EXISTS <ClonedTableName>(like <OriginalTableName> including all)
well in mysql ,both is possible in one command
the command is
create table new_tbl (PRIMARY KEY(`id`)) as select * from old_tbl;
where id is column with primary key of old_tbl
done...
You may do this way
CREATE TABLE IOT (EMPID,ID,Name, CONSTRAINT PK PRIMARY KEY( ID,EMPID))
ORGANIZATION INDEX NOLOGGING COMPRESS 1 PARALLEL 4
AS SELECT 1 as empid,2 id,'XYZ' Name FROM dual;