Having a table with a columnn ID as primary key, and a column MyNumber that contains integers defined by the sequence myUniqueSequence. I would like to define myUniqueSequence in PostgreSQL that will return the next free and unique number for the column MyNumber.
This means, the next time a new row is created programatically will start by number 1, if it's free it will use it for the column myNumber, if not, it tries with 2 and so on.
Use the serial data type for your column (instead of your own sequence):
http://www.postgresql.org/docs/9.0/static/datatype-numeric.html#DATATYPE-SERIAL
Related
I built a db with serial type for the pks, I migrated to another server and the pk columns are now integer and as a result I cannot add new data due to the not null restriction of a pk. Is there any Alter command which can fix this?
SERIAL is not a data type in postgresql just a convenience word when creating tables that makes the column an integer type and adds auto-incrementing. All you have to do is add back auto-incrementing (a sequence) to the column and make sure its next value is greater than anything in the table.
This question covers adding serial to an existing column
This answer explains how to reset the counter
I am a little confused and new to PostgreSql , I thought that serial = integer and bigserial = bigint, so I am confused why I see a sequence with a max val of 9223372036854775807 instead of 2147483647, when I create a table with a PK that is serial.
As stated in the PostgreSQL 9.4 docs for Data Type SERIAL a sequence is implicitly created using CREATE SEQUENCE tablename_colname_seq without any additional parameters.
The documentation for CREATE SEQUENCE says:
The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If this clause is not supplied or NO MAXVALUE is specified, then default values will be used. The defaults are 2^63-1 and -1 for ascending and descending sequences, respectively.
So it is documented behaviour that the sequence is created with the max value you are seing.
The sequence and the column are two separate things. A sequence could return an integer larger than an int4 column could store. When you specify SERIAL or BIGSERIAL, PostgreSQL roughly translates that into:
create an int4 or int8 column
create a sequence
make the sequence owned by the column
make the column default value the next value from the sequence
SERIAL is a convenience, but there is not an actual column type SERIAL.
As the title suggests I want to have a unique ID as a primary key but over multiple schemas. I know about UUID but it's just too costly.
Is there any way to work this around a serial?
You can create a global sequence and use that in your table instead of the automatic sequence that a serial column creates.
create schema global;
create schema s1;
create schema s2;
create sequence global.unique_id;
create table s1.t1
(
id integer default nextval('global.unique_id') primary key
);
create table s2.t1
(
id integer default nextval('global.unique_id') primary key
);
The difference to a serial column is, that the sequence unique_id doesn't "know" it's used by the id columns. A "serial sequence" is automatically dropped if the corresponding column (or table) is dropped which is not what you want with a global sequence.
There is one drawback however: you can't make sure that duplicate values across those two table are inserted manually. If you want to make sure the sequence is always used to insert values, you can create a trigger that always fetches a value from the sequence.
I've created table projects like so:
CREATE TABLE projects (
project_id NUMBER(10,0) GENERATED BY DEFAULT ON NULL AS IDENTITY ,
project_name VARCHAR2(75 CHAR) NOT NULL
Then I've inserted ~150,000 rows while importing data from my old MySQL table. the MySQL had existing id numbers which i need to preserve so I added the id number to the SQL during the insert. Now when I insert new rows into the oracle table, the id is a very low number. Can you tell me how to reset my counter on the project_id column to start at 150,001 so not to mess up any of my existing id numbers? essentially i need the oracle version of:
ALTER TABLE tbl AUTO_INCREMENT = 150001;
Edit: Oracle 12c now supports the identity data type, allowing an auto number primary key that does not require us to create a sequence + insert trigger.
SOLUTION:
after some creative google search terms I was able to find this thread on the oracle docs site. here is the solution for changing the identity's nextval:
ALTER TABLE projects MODIFY project_id GENERATED BY DEFAULT ON NULL AS IDENTITY ( START WITH 150000);
Here is the solution that i found on this oracle thread:. The concept is to alter your identity column rather than adjust the sequence. Actually, the sequences that are automatically created aren't editable or drop-able.
ALTER TABLE projects MODIFY project_id GENERATED BY DEFAULT ON NULL AS IDENTITY ( START WITH 150000);
According to this source, you can do it like this:
ALTER TABLE projects MODIFY project_id
GENERATED BY DEFAULT ON NULL AS IDENTITY (START WITH LIMIT VALUE);
The START WITH LIMIT VALUE clause can only be specified with an ALTER TABLE statement (and by implication against an existing identity column). When this clause is specified, the table will be scanned for the highest value in the PROJECT_ID column and the sequence will commence at this value + 1.
The same is also stated in the oracle thread referenced in OP's own answer:
START WITH LIMIT VALUE, which is specific to identity_options, can only be used with ALTER TABLE MODIFY. If you specify START WITH LIMIT VALUE, then Oracle Database locks the table and finds the maximum identity column value in the table (for increasing sequences) or the minimum identity column value (for decreasing sequences) and assigns the value as the sequence generator's high water mark. The next value returned by the sequence generator will be the high water mark + INCREMENT BY integer for increasing sequences, or the high water mark - INCREMENT BY integer for decreasing sequences.
The following statement creates the sequence customers_seq in the sample schema oe. This sequence could be used to provide customer ID numbers when rows are added to the customers table.
CREATE SEQUENCE customers_seq
START WITH 1000
INCREMENT BY 1
NOCACHE
NOCYCLE;
The first reference to customers_seq.nextval returns 1000. The second returns 1001. Each subsequent reference will return a value 1 greater than the previous reference.
http://docs.oracle.com/cd/B12037_01/server.101/b10759/statements_6014.htm
I thought this would be simple, but I can't seem to use AUTO_INCREMENT in my db2 database. I did some searching and people seem to be using "Generated by Default", but this doesn't work for me.
If it helps, here's the table I want to create with the sid being auto incremented.
create table student(
sid integer NOT NULL <auto increment?>
sname varchar(30),
PRIMARY KEY (sid)
);
Any pointers are appreciated.
You're looking for is called an IDENTITY column:
create table student (
sid integer not null GENERATED ALWAYS AS IDENTITY (START WITH 1 INCREMENT BY 1)
,sname varchar(30)
,PRIMARY KEY (sid)
);
A sequence is another option for doing this, but you need to determine which one is proper for your particular situation. Read this for more information comparing sequences to identity columns.
You will have to create an auto-increment field with the sequence object (this object generates a number sequence).
Use the following CREATE SEQUENCE syntax:
CREATE SEQUENCE seq_person
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10
The code above creates a sequence object called seq_person, that starts with 1 and will increment by 1. It will also cache up to 10 values for performance. The cache option specifies how many sequence values will be stored in memory for faster access.
To insert a new record into the "Persons" table, we will have to use the nextval function (this function retrieves the next value from seq_person sequence):
INSERT INTO Persons (P_Id,FirstName,LastName)
VALUES (seq_person.nextval,'Lars','Monsen')
The SQL statement above would insert a new record into the "Persons" table. The "P_Id" column would be assigned the next number from the seq_person sequence. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".
hi If you are still not able to make column as AUTO_INCREMENT while creating table. As a work around first create table that is:
create table student(
sid integer NOT NULL
sname varchar(30),
PRIMARY KEY (sid)
);
and then explicitly try to alter column bu using the following
alter table student alter column sid set GENERATED BY DEFAULT AS
IDENTITY
Or
alter table student alter column sid set GENERATED BY DEFAULT
AS IDENTITY (start with 100)
Added a few optional parameters for creating "future safe" sequences.
CREATE SEQUENCE <NAME>
START WITH 1
INCREMENT BY 1
NO MAXVALUE
NO CYCLE
CACHE 10;