I am with PostgreSQL 9.5 X64 integrated with the open-source Parse Server. My table has the following structure.
objectId (text with fixed 10 characters),
item_id (integer),
item_name (text with various length)
The objectId is the primary key due to use of Parse Server. It is automatically generated by Parse Server. The item_id is not a primary key. I would like to have item_id automatically increment by 1 when a new record is created. How can this be achieved in Create Table?
Add a default value with a sequence:
CREATE SEQUENCE mytable_item_id_seq OWNED BY mytable. item_id;
ALTER TABLE mytable ALTER item_id SET DEFAULT nextval('mytable_item_id_seq');
To make that work, you have to exclude the item_id column from all INSERT statrments, because the default value is only used if no value is specified for the column.
You may try making the item_id column SERIAL. I don't know whether or not it's possible to alter the current item_id column to make it serial, so we might have to drop that column and then add it back, something like this:
ALTER TABLE yourTable DROP COLUMN item_id;
ALTER TABLE yourTable ADD COLUMN item_id SERIAL;
If there is data in the item_id column already, it may not make sense from a serial point of view, so hopefully there is no harm in deleting it.
Related
I have a problem with a really big database with following scheme:
id | date | other columns...
The id column is from type integer. It would be ideal if it where from type integer with a nextval constraint. Many of the id entries have unique id's incremented when they where added.
The problem is all rows added since a specific date have no id and the value is null.
Is it possible to add such constraints to tables with existing values (plus null values) so that the null values are filled with integer id's?
And is this possible without losing the old id's and in the best case with ascending order in relation to the date column?
thanks and greetings
You need to first update the existing rows with a unique, non-null value:
update the_table
set id = new_id
from (
select ctid,
(select max(id) from the_table) + row_number() over (order by date) as new_id
from the_table
where id is null
) t
where t.ctid = the_table.ctid;
I am not sure if the order of the IDs is guaranteed using this approach, but it's likely that it does.
Now, that the column doesn't contain any NULL values, we can either change it automatically assign new values.
The next steps depend on whether you want to make this an identity column or simply a column with a default from a sequence (essentially a (discouraged) serial column)
Staying with a "serial"
We need to create a sequence and sync it with the highest value in the column.
create sequence the_table_id_seq;
select setval('the_table_id_seq', max(id))
from the_table;
Then use this for the default and link the sequence to the column.
alter table the_table
alter id set not null,
alter id set default nextval('the_table_id_seq') ;
alter sequence the_table_id_seq owned by the_table.id;
Using an identity column (recommended)
To make this a proper (recommended) identity column (Postgres 10 and later) you can do it like this:
alter table the_table
alter id set not null,
alter id add generated always as identity;
Now adding the identity attribute created a new sequence which we need to sync with the existing values in the column:
select setval(pg_get_serial_sequence('the_table', 'id'), max(id))
from the_table;
Alternatively, you could have manually looked up the current max value and provide that directly when specifying the identity default:
alter table the_table
alter id set not null,
alter id add generated always as identity (start with 42);
Is it possible to add an autogenerated primary key column ( timestamp) to the existing table with alter table?
Something like this but it doesn't compile
ALTER TABLE DB2ADMIN.xxxyyyy ADD COLUMN ID TIMESTAMP NOT NULL WITH DEFAULT timestamp(generate_unique())#
Error during Prepare
42601(-104)[IBM][CLI Driver][DB2/AIX64] SQL0104N An unexpected token "timestamp" was found following "OT NULL WITH DEFAULT". Expected tokens may include: "CHECK". SQLSTATE=42601
It is unwise to use a fake (from generate_unique) timestamp datatype as a primary key because it makes setting values for pre-existing rows more awkward, and makes date arithmetic impossible.
The datatype TIMESTAMP is better suited for real dates/times because then you can use date arithmetic, which is practical for business. If the values in your fake timestamp-column are from generate-unique then you cannot sensibly use date arithmetic.
If you try to use a real timestamp value , (instead of generate_unique) , such as current timestamp then you are likely to get collisions, depending on the insert-rate. Usually that's a bad idea. Also this makes setting values for any pre-existing rows more difficult.
It is usually much easier and faster to use an autogenerated identity column as a surrogate primary key, especially if the table already has existing data.
Here is a typical way to do this which works with Db2-LUW and also on older versions of Db2. Other ways are possible with later versions of Db2.
Firs you need to verify that the table does not already have a primary key, as there can only be at most one of these per table.
Next, check if the table already has a unique index on a NOT NULL column, because if such a column exists then it can be promoted to be the primary key column.
If neither of the above exist, then you can use logic like this below to add an autgenerated column, set unique values in any existing rows, and ensure that any future inserts automatically get a unique value in the column without application intervention.
alter table myschema.mytab add column id bigint not null default 0 ;
alter table myschema.mytab alter column id drop default ;
alter table myschema.mytab alter column id set generated always as identity ;
update myschema.mytab set id = default ;
alter table myschema.mytab add constraint pkey primary key(id) ;
reorg table myschema.mytab ;
runstats on table myschema.mytab with distribution and detailed indexes all;
You can use CURRENT_TIMESTAMP instead of timestamp(generate_unique())
ALTER TABLE sellers ADD COLUMN ID TIMESTAMP NOT NULL WITH DEFAULT CURRENT_TIMESTAMP
You can test here
I have a H2 database with 16 million entries and no primary key. I successfully added an auto-incrementing primary key using the following statements:
ALTER TABLE
PUBLIC.ADDRESSES ADD ID BIGINT AUTO_INCREMENT;
ALTER TABLE
PUBLIC.ADDRESSES ADD PRIMARY KEY (ID)
Now the problem is, that the column order is STREET, HOUSENUMBER, ..., ID, but I would like ID to be the first column of the table. It looks like there is a corresponding ALTER TABLE statement MySQL (see here), but I'm unable to adapt it to H2.
Long story short: How can I change the column order to ID, STREET, HOUSENUMBER ...? Is there a solution similar to:
ALTER TABLE "ADDRESSES" MODIFY COLUMN "ID" BEFORE "STREET";
Any help is kindly appreciated.
H2 does not currently support re-ordering columns. You would need to run multiple statements:
First, rename the column, then add a new column with the right name at the right position (alter table add supports positioning), and finally drop the old column.
Or, probably more elegant, use rename table and then create table ... as select.
I am using Netbeans, writing in Java and using Derby.
I have a table within APP called PERSON. Within PERSON I have a column called PID with the following properties:
Name: PID
Nulls allowed: [ ]
Data type: NUMERIC
Column size: 4
Decimal digits: 0
Position: 1
Part of a primary key: [/]
Part of an index: [/]
I used the meta data isAutoIncrement function to check if it was already auto incrementing and it is not!
I have since tried using the following SQL commands to alter it:
I believe this may not have been for Derby:
ALTER TABLE APP.PERSON ALTER PID NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY
(START WITH 1, INCREMENT BY 1);
Upon checking the Oracle website, I found the correct syntax:
ALTER TABLE APP.PERSON ALTER PID SET INCREMENT BY 1;
I even tried leading zeros:
ALTER TABLE APP.PERSON ALTER PID SET INCREMENT BY 0001;
None of which have worked, the error I get on the last two are:
ALTER TABLE '"APP"."PERSON"' specified attributes for column 'PID' that are
not compatible with the existing column.
Any ideas of the correct syntax?
Here's what I generally do to accomplish this:
Create a new table, with the desired schema, including the generated primary key
Issue a INSERT INTO newtable SELECT columns FROM oldtable to populate the new table's data from the old table
Rename the old table to some temporary name, like table_soon_to_be_deleted
Rename the new table to the desired table name
Do some testing to make sure that my behavior is as expected
Drop the old table that I renamed in step (4).
JavaDB does not allow altering a column with generated key word so I found the best way is to recreate the table and specify the primary key as auto incremented. For example;
create table staff(
ID int primary key always generated as identity,
name varchar(100)
);
This worked for me.
How to change the type of a column in a SQLite table?
I've got:
CREATE TABLE table(
id INTEGER,
salt TEXT NOT NULL UNIQUE,
step INT,
insert_date TIMESTAMP
);
I'd like to change salt's type to just TEXT and id's type to INTEGER PRIMARY KEY.
Below is an excerpt from the SQLite manual discussing the ALTER TABLE command (see URL: SQLite Alter Table):
SQLite supports a limited subset of
ALTER TABLE. The ALTER TABLE command
in SQLite allows the user to rename a
table or to add a new column to an
existing table. It is not possible to
rename a colum, remove a column, or
add or remove constraints from a
table.
As the manual states, it is not possible to modify a column's type or constraints, such as converting NULL to NOT NULL. However, there is a work around by
copying the old table to a temporary table,
creating a new table defined as desired, and
copying the data from the temporary table to the new table.
To give credit where credit is due, I learned this from the discussion on Issue #1 of hakanw's django-email-usernames project on bitbucket.org.
CREATE TABLE test_table(
id INTEGER,
salt TEXT NOT NULL UNIQUE,
step INT,
insert_date TIMESTAMP
);
ALTER TABLE test_table RENAME TO test_table_temp;
CREATE TABLE test_table(
id INTEGER PRIMARY KEY,
salt TEXT,
step INT,
insert_date TIMESTAMP
);
INSERT INTO test_table SELECT * FROM test_table_temp;
DROP TABLE test_table_temp;
Notes
I used the table name test_table since SQLite will generate an error if you try to name a table as table.
The INSERT INTO command will fail if your data does not conform to the new table constraints. For instance, if the original test_table contains two id fields with the same integer, you will receive an "SQL error: PRIMARY KEY must be unique" when you execute the "INSERT INTO test_table SELECT * FROM test_table_temp;" command.
For all testing, I used SQLite version 3.4.0 as included as part of Python 2.6.2 running on my 13" Unibody MacBook with Mac OS X 10.5.7.
Since RDBMS is not specified, these are DB2 queries:
Make ID as primary key:
ALTER TABLE table
ADD CONSTRAINT pk_id
PRIMARY KEY (id)
Make salt as not UNIQUE:
ALTER TABLE table
DROP UNIQUE <salt-unique-constraint-name>
Make salt nullable:
ALTER TABLE table
ALTER COLUMN salt DROP NOT NULL
You will need to do a reorg after drop not null. This is to be done from the command prompt.
reorg table <tableName>
In this case you can make salt to nullable and remove unique constraint. Also If id column does not contain any null or duplicate values you can safely make it primary key using sql server management studio. below is the screen shot. hope it makes it clearer:
alt text http://img265.imageshack.us/img265/7418/91573473.png
or use following sql:
alter table <TableName> modify salt text null
alter table <TableName> drop constraint <Unique Constraint Name>
alter table <TableName> modify id int not null
alter table <TableName> add constraint pk<Table>d primary key (id)