In Postgres, defining a column with SERIAL/BIGSERIAL has a triple effect as discussed here:
Define a int/bigint column.
Create a sequence object to generate auto-incrementing numbers.
Set the default of the column to call nextval() on the sequence.
Is there a similar shortcut command in H2 to get this related set of behavior?
If not, what would the long version of the SQL be?
Where does the sequence live? How can you adjust its value or reset it?
If you create a column as auto_increment (or identity) H2 creates a sequence in the background. The name of that sequence can be obtained by looking at information_schema.columns:
create table foo
(
id integer auto_increment,
other_column varchar(20)
);
If you then run:
select column_name, column_default
from information_schema.columns
where table_name = 'FOO'
and table_schema = 'PUBLIC';
You'll get something like this:
COLUMN_NAME | COLUMN_DEFAULT
-------------+-----------------------------------------------------------------------------
ID | (NEXT VALUE FOR PUBLIC.SYSTEM_SEQUENCE_C1C36118_ED1C_44D6_B573_6C00C5923EAC)
OTHER_COLUMN |
You can alter that sequence without problems:
alter sequence SYSTEM_SEQUENCE_C1C36118_ED1C_44D6_B573_6C00C5923EAC
restart with 42;
This is essentially identical to Postgres' serial data type
If not, what would the long version of the SQL be?
create sequence foo_id_seq;
create table foo
(
id integer default foo_id_seq.nextval,
other_column varchar(20)
);
The big difference between this and a Postgres serial is that H2 does not know that the sequence "belongs" to the column. You need to drop it manually when the table is dropped.
foo_id_seq.nextval will actually be converted to (NEXT VALUE FOR PUBLIC.FOO_ID_SEQ) when the table is created (and it will be stored like that in information_schema.columns.
Related
I was wondering how can I add an identity column to existing oracle table? I am using oracle 11g. Suppose I have a table named DEGREE and I am going to add an identity column to that.
FYI table is not empty.
You can not do it in one step. Instead,
Alter the table and add the column (without primary key constraint)
ALTER TABLE DEGREE ADD (Ident NUMBER(10));
Fill the new column with data which will fulfill the primary key constraint (unique/not null), e.g. like
UPDATE DEGREE SET Ident=ROWNUM;
Alter the table and add the constraint to the column
ALTER TABLE DEGREE MODIFY (Ident PRIMARY KEY);
After that is done, you can set up a SEQUENCE and a BEFORE INSERT trigger to automatically set the id value for new records.
From Oracle 12c you would use an identity column.
For example, say your table is called demo and has 3 columns and 100 rows:
create table demo (col1, col2, col3)
as
select dbms_random.value(1,10), dbms_random.value(1,10), dbms_random.value(1,10)
from dual connect by rownum <= 100;
You could add an identity column using:
alter table demo add demo_id integer generated by default on null as identity;
update demo set demo_id = rownum;
Then reset the internal sequence to match the data and prevent manual inserts:
alter table demo modify demo_id generated always as identity start with limit value;
and define it as the primary key:
alter table demo add constraint demo_pk primary key (demo_id);
This leaves the new column at the end of the column list, which shouldn’t normally matter (except for tables with a large number of columns and row chaining issues), but it looks odd when you describe the table. However, we can at least tidy up the dictionary order using the invisible/visible hack:
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
DEMO_ID NOT NULL NUMBER(38)
begin
for r in (
select column_name from user_tab_columns c
where c.table_name = 'DEMO'
and c.column_name <> 'DEMO_ID'
order by c.column_id
)
loop
execute immediate 'alter table demo modify '||r.column_name||' invisible';
execute immediate 'alter table demo modify '||r.column_name||' visible';
end loop;
end;
/
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
DEMO_ID NOT NULL NUMBER(38)
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
One thing you can't do (as of Oracle 18.0) is alter an existing column to make it into an identity column, so you have to either go through a process like the one above but copying the existing values and finally dropping the old column, or else define a new table explicitly with the identity column in place and copy the data across in a separate step. Otherwise you'll get:
-- DEMO_ID column exists but is currently not an identity column:
alter table demo modify demo_id generated by default on null as identity start with limit value;
-- Fails with:
ORA-30673: column to be modified is not an identity column
add the column
alter table table_name add (id INTEGER);
create a sequence table_name_id_seq with start with clause, using number of rows in the table + 1 or another safe value(we don't want duplicate ids);
lock the table (no inserts)
alter table table_name lock exclusive mode;
fill the column
update table_name set id = rownum; --or another logic
add a trigger to automaticaly put the id on insert using the sequence(you can find examples on internet, for example this answer)
When you'll fire the create trigger the lock will be released. (it automatically commits).
Also, you may add unique constraint on the id column, it is best to do so.
For Oracle :
CREATE TABLE new_table AS (SELECT ROWNUM AS id, ta.* FROM old_table ta)
remember this id column is not auto incremented
Here is a question about changing serial value with alter key word. Can this be done in create table defintion? Like that:
CREATE TABLE tablename (
colname SERIAL stars 1000
);
You can try this query.Its worked for me.
CREATE SEQUENCE tablename_colname_seq
INCREMENT 1
MINVALUE 1
MAXVALUE 9223372036854775807
START 1 ---> here you can mention startup nummber as you need
CACHE 1;
CREATE TABLE tablename (
colname integer NOT NULL DEFAULT nextval('tablename_colname_seq')
);
Identity Columns
There is no currently no way to do this in a CREATE TABLE command in PostgreSQL 9.x using the PostgreSQL-specific serial-type syntax. However, it's coming in PostgreSQL 10 using the standardized Identity Columns syntax, see my answer on it here
Here is how it will look
CREATE TABLE foo (
id int GENERATED { ALWAYS | BY DEFAULT }
AS IDENTITY [ ( sequence_options ) ]
);
Where (sequence_options) is START WITH 1000, so something like this.
CREATE TABLE foo (
foo_id int GENERATED ALWAYS AS IDENTITY (START WITH 1000)
);
I have like 11 columns in my database table and i am inserting data in 10 of them. i want to have a unique number like "1101 and so on" in the 11th column.
Any idea what should i do?? Thanks in advance.
SQL Server 2012 and above you can generate Sequence
Create SEQUENCE RandomSeq
start with 1001
increment by 1
Go
Insert into YourTable(Id,col1...)
Select NEXT VALUE FOR RandomSeq,col1....
or else you can use Identity
Identity(seed,increment)
You can start the seed from 1101 and increment the sequence by 1
Create table YourTable
(
id INT IDENTITY(1101,1),
Col varchar(10)
)
If you want to have that unique number in a different field then you can manipulate that field with primary key and insert that value.
If you want in primary key value, then open the table in design mode, go to 'Identity specification', set 'identity increment' and 'identity seed' as you want.
Alternatively you can use table script like,
CREATE TABLE Persons
(
ID int IDENTITY(12,1) PRIMARY KEY,
FName varchar(255) NOT NULL,
)
here the primary key will start seeding from 12 and seed value will be 1.
If you have your table definition already in place you can alter the column and add Computed column marked as persisted as:
ALTER TABLE tablename drop column column11;
ALTER TABLE tablename add column11 as '11'
+right('000000'+cast(ID as varchar(10)), 2) PERSISTED ;
--You can change the right operator value from 2 to any as per the requirements.
--Also replace ID with the identity column in your table.
create table inc
(
id int identity(1100,1),
somec char
)
Okay no seriously, if a PostgreSQL guru can help out I'm just getting started.
Basically what I want is a simple table like such:
CREATE TABLE schema.searches
(
search_id serial NOT NULL,
search_query character varying(255),
search_count integer DEFAULT 1,
CONSTRAINT pkey_search_id PRIMARY KEY (search_id)
)
WITH (
OIDS=FALSE
);
I need something like REPLACE INTO for MySQL. I don't know if I have to write my own procedure or something?
Basically:
check if the query already exists
if so, just add 1 to the count
it not, add it to the db
I can do this in my php code but I'd rather all that be done in postgres C engine
You have to add a unique constraint first.
ALTER TABLE schema.searches ADD UNIQUE (search_query);
The insert/replace command looks like this.
INSERT INTO schema.searches(search_query) VALUES ('a search query')
ON CONFLICT (search_query)
DO UPDATE SET search_count = schema.searches.search_count + 1;
In PostgreSql, one can define a sequence and use it as the primary key of a table. In HsqlDB, one can still accomplish creating an auto-increment identity column which doesn't link to any user defined sequence. Is it possible to use a user defined sequence as the generator of an auto-increment identity column in HsqlDB?
Sample sql in PostgreSql:
CREATE SEQUENCE seq_company_id START WITH 1;
CREATE TABLE company (
id bigint PRIMARY KEY DEFAULT nextval('seq_company_id'),
name varchar(128) NOT NULL CHECK (name <> '')
);
What's the equivalent in HsqlDB?
Thanks.
In version 2.0, there is no direct feature for this. You can define a BEFORE INSERT trigger on the table to do this:
CREATE TABLE company ( id bigint PRIMARY KEY, name varchar(128) NOT NULL CHECK (name <> '') );
CREATE TRIGGER trigg BEFORE INSERT
ON company REFERENCING NEW ROW AS newrow
FOR EACH ROW
SET newrow.id = NEXT VALUE FOR seq_company_id;
and insert without using any vlue for id
INSERT INTO company VALUES null, 'test'
Update for HSQLDB 2.1 and later: A feature has been added to support this.
CREATE SEQUENCE SEQU
CREATE TABLE company ( id bigint GENERATED BY DEFAULT AS SEQUENCE SEQU PRIMARY KEY, name varchar(128) NOT NULL CHECK (name <> '') );
See the Guide under CREATE TABLE http://hsqldb.org/doc/2.0/guide/databaseobjects-chapt.html#dbc_table_creation
In addition, 2.1 and later has a PostgreSQL compatibility mode in which it accepts the PostgreSQL CREATE TABLE statement that references the sequence in the DEFAULT clause and translates it to HSQLDB syntax.