I'm using Grails 3.0.7 and Postgres 9.2. I'm very new to Postgres, so this may be a dumb question. How do I correctly associate an id generator sequence with a table? I read somewhere that if you create a table with an id column that has a serial datatype, then it will automatically create a sequence for that table.
However, the column seems to be created with a type of bigint. How do I get Grails to create the column with a bigserial datatype, and will this even solve my problem? What if I want one sequence per table? I'm just not sure how to go about setting this up because I've never really used Postgres in the past.
You can define a generator in a domain class like this:
static mapping = {
id generator:'sequence', params:[sequence:'domain_sq']
}
If the sequence is already present in the database then you'll need to name it in the params.
There are other properties also available as outlined in the documentation, for example:
static mapping = {
id column: 'book_id', type: 'integer'
}
In Postgres 10 or later consider an IDENTITY column instead. See:
Auto increment table column
However, the column seems to be created with a type of bigint. How do
I get Grails to create the column with a bigserial datatype, and will
this even solve my problem?
That's expected behavior. Define the column as bigserial, that's all you have to do. The Postgres pseudo data types smallserial, serial and bigserial create a smallint, int or bigint column respectively, and attach a dedicated sequence. The manual:
The data types smallserial, serial and bigserial are not true types,
but merely a notational convenience for creating unique identifier
columns (similar to the AUTO_INCREMENT property supported by some
other databases). In the current implementation, specifying:
CREATE TABLE tablename (
colname SERIAL
);
is equivalent to specifying:
CREATE SEQUENCE tablename_colname_seq;
CREATE TABLE tablename (
colname integer NOT NULL DEFAULT nextval('tablename_colname_seq')
);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;
Big quote, I couldn't describe it any better than the manual.
Related:
Get table and column "owning" a sequence
Safely rename tables using serial primary key columns
Related
In a Postgres 9.3 table I have an integer as primary key with automatic sequence to increment, but I have reached the maximum for integer. How to convert it from integer to serial?
I tried:
ALTER TABLE my_table ALTER COLUMN id SET DATA TYPE bigint;
But the same does not work with the data type serial instead of bigint. Seems like I cannot convert to serial?
serial is a pseudo data type, not an actual data type. It's an integer underneath with some additional DDL commands executed automatically:
Create a SEQUENCE (with matching name by default).
Set the column NOT NULL and the default to draw from that sequence.
Make the column "own" the sequence.
Details:
Safely rename tables using serial primary key columns
A bigserial is the same, built around a bigint column. You want bigint, but you already achieved that. To transform an existing serial column into a bigserial (or smallserial), all you need to do is ALTER the data type of the column. Sequences are generally based on bigint, so the same sequence can be used for any integer type.
To "change" a bigint into a bigserial or an integer into a serial, you just have to do the rest by hand:
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
The actual data type is still integer / bigint. Some clients like pgAdmin will display the data type serial in the reverse engineered CREATE TABLE script, if all criteria for a serial are met.
In a Postgres 9.3 table I have an integer as primary key with automatic sequence to increment, but I have reached the maximum for integer. How to convert it from integer to serial?
I tried:
ALTER TABLE my_table ALTER COLUMN id SET DATA TYPE bigint;
But the same does not work with the data type serial instead of bigint. Seems like I cannot convert to serial?
serial is a pseudo data type, not an actual data type. It's an integer underneath with some additional DDL commands executed automatically:
Create a SEQUENCE (with matching name by default).
Set the column NOT NULL and the default to draw from that sequence.
Make the column "own" the sequence.
Details:
Safely rename tables using serial primary key columns
A bigserial is the same, built around a bigint column. You want bigint, but you already achieved that. To transform an existing serial column into a bigserial (or smallserial), all you need to do is ALTER the data type of the column. Sequences are generally based on bigint, so the same sequence can be used for any integer type.
To "change" a bigint into a bigserial or an integer into a serial, you just have to do the rest by hand:
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
The actual data type is still integer / bigint. Some clients like pgAdmin will display the data type serial in the reverse engineered CREATE TABLE script, if all criteria for a serial are met.
I've got a PgSQL 9.4.3 server setup and previously I was only using the public schema and for example I created a table like this:
CREATE TABLE ma_accessed_by_members_tracking (
reference bigserial NOT NULL,
ma_reference bigint NOT NULL,
membership_reference bigint NOT NULL,
date_accessed timestamp without time zone,
points_awarded bigint NOT NULL
);
Using the Windows Program PgAdmin III I can see it created the proper information and sequence.
However I've recently added another schema called "test" to the same database and created the exact same table, just like before.
However this time I see:
CREATE TABLE test.ma_accessed_by_members_tracking
(
reference bigint NOT NULL DEFAULT nextval('ma_accessed_by_members_tracking_reference_seq'::regclass),
ma_reference bigint NOT NULL,
membership_reference bigint NOT NULL,
date_accessed timestamp without time zone,
points_awarded bigint NOT NULL
);
My question / curiosity is why in a public schema the reference shows bigserial but in the test schema reference shows bigint with a nextval?
Both work as expected. I just do not understand why the difference in schema's would show different table creations. I realize that bigint and bigserial allow the same volume of ints to be used.
Merely A Notational Convenience
According to the documentation on Serial Types, smallserial, serial, and bigserial are not true data types. Rather, they are a notation to create at once both sequence and column with default value pointing to that sequence.
I created test table on schema public. The command psql \d shows bigint column type. Maybe it's PgAdmin behavior ?
Update
I checked PgAdmin source code. In function pgColumn::GetDefinition() it scans table pg_depend for auto dependency and when found it - replaces bigint with bigserial to simulate original table create code.
When you create a serial column in the standard way:
CREATE TABLE new_table (
new_id serial);
Postgres creates a sequence with commands:
CREATE SEQUENCE new_table_new_id_seq ...
ALTER SEQUENCE new_table_new_id_seq OWNED BY new_table.new_id;
From documentation: The OWNED BY option causes the sequence to be associated with a specific table column, such that if that column (or its whole table) is dropped, the sequence will be automatically dropped as well.
Standard name of a sequence is built from table name, column name and suffix _seq.
If a serial column was created in such a way, PgAdmin shows its type as serial.
If a sequence has non-standard name or is not associated with a column, PgAdmin shows nextval() as default value.
In a Postgres 9.3 table I have an integer as primary key with automatic sequence to increment, but I have reached the maximum for integer. How to convert it from integer to serial?
I tried:
ALTER TABLE my_table ALTER COLUMN id SET DATA TYPE bigint;
But the same does not work with the data type serial instead of bigint. Seems like I cannot convert to serial?
serial is a pseudo data type, not an actual data type. It's an integer underneath with some additional DDL commands executed automatically:
Create a SEQUENCE (with matching name by default).
Set the column NOT NULL and the default to draw from that sequence.
Make the column "own" the sequence.
Details:
Safely rename tables using serial primary key columns
A bigserial is the same, built around a bigint column. You want bigint, but you already achieved that. To transform an existing serial column into a bigserial (or smallserial), all you need to do is ALTER the data type of the column. Sequences are generally based on bigint, so the same sequence can be used for any integer type.
To "change" a bigint into a bigserial or an integer into a serial, you just have to do the rest by hand:
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
The actual data type is still integer / bigint. Some clients like pgAdmin will display the data type serial in the reverse engineered CREATE TABLE script, if all criteria for a serial are met.
I have a table with 8440 records with a natural (string) primary key. Now I just discovered that to support a legacy client, I need the records to have integer keys as well. what's the easiest way to add a serial INT column to this table with a unique constraint and populate it with integer values from 1 to 8440?
Alter the table, add a new not null column of type serial, with a unique key on it.
In Postgres, the serial type is a mere alias for the int type with a default value of nextval(some_sequence), the latter of which is created on the fly.