I made a mistake by the creation of my table. The primary key was incorrect. I delete the constraint and now I don't have a primary key in my table, only the field with the data. Now I want to set again this field as auto_increment primary key without losing my data. How I can do this?
I tryed this:
ALTER TABLE name_table ADD COLUMN name_column serial primary key;
But with this I am losing my data and creating a new column, that I don't want
try this
ALTER TABLE table_name ADD CONSTRAINT some_name primary key (name_column);
For my suggestion,
backup your database first in sql or csv or xml or excel something
restore-able.
Then alter your table structure, column data type, from UI or command
Then if data recorded on your table are lost or gone, restore your
backup data only, (not the structure of table)
After that you have changed column data type and also get your required data. I hope it will work.
Hi guys I was trying several ways and I found this one and maybe also somebody later can use:
Create a sequenz: Sequenz is the way that Postgresql implement to generate auto_increment fields. Ones we have a auto_increment is also a primary key. Should not be like this, is not a rule, but in most of the cases a auto_increment field is a primary key.
To create a sequenz is like this:
CREATE SEQUENCE exemplo_id_seq
INCREMENT 1 --the increment upgrate will be made 1 + 1
MINVALUE 1
MAXVALUE
START 1 --the start counting is in 1
CACHE 1;
After this is only to give this sequenz to the affected field using NEXTVAL, like this:
ALTER TABLE table_name ALTER COLUMN id SET DEFAULT NEXTVAL("exemplo_id_seq"::regclass);
Is working good without losing the data from old errors
Related
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;
I'm switching from MongoDB to PostgreSQL and was wondering how I can implement the same concept as used in MongoDB for uniquely identifying each raws by MongoId.
After migration, the already existing unique fields in our database is saved as character type. I am looking for minimum source code changes.
So if any way exist in postgresql for generating auto increment unique Id for each inserting into table.
The closest thing to MongoDB's ObjectId in PostgreSQL is the uuid type. Note that ObjectId has only 12 bytes, while UUIDs have 128 bits (16 bytes).
You can convert your existsing IDs by appending (or prepending) f.ex. '00000000' to them.
alter table some_table
alter id_column
type uuid
using (id_column || '00000000')::uuid;
Although it would be the best if you can do this while migrating the schema + data. If you can't do it during the migration, you need to update you IDs (while they are still varchars: this way the referenced columns will propagate the change), drop foreign keys, do the alter type and then re-apply foreign keys.
You can generate various UUIDs (for default values of the column) with the uuid-ossp module.
create extension "uuid-ossp";
alter table some_table
alter id_column
set default uuid_generate_v4();
Use a sequence as a default for the column:
create sequence some_id_sequence
start with 100000
owned by some_table.id_column;
The start with should be bigger then your current maximum number.
Then use that sequence as a default for your column:
alter table some_table
alter id_column set default nextval('some_id_sequence')::text;
The better solution would be to change the column to an integer column. Storing numbers in a text (or varchar) column is a really bad idea.
My table has three rows and i don't want to add any more rows.
However i want to be able to select & update on the table.
What is the best way to block further inserts ?
Assuming you have a primary key named id with the current values 1,2 and 3 you could do something like this:
alter table the_table
add constraint limit_values check (id in (1,2,3));
Now if you try to insert a new row, you either get a primary key violation (because 1,2 and 3 already exist) or you get a check constraint violation when you try to insert a different ID value that does not yet exist.
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;
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;