I am unable to set the max size of particular column in PostgreSQL with MAX keyword. Is there any keyword like MAX. If not how can we create the column with the maximum size?
If you want to created an "unbounded" varchar column just use varchar without a length restriction.
From the manual:
If character varying is used without length specifier, the type accepts strings of any size
So you can use:
create table foo
(
unlimited varchar
);
Another alternative is to use text:
create table foo
(
unlimited text
);
More details about character data types are in the manual:
http://www.postgresql.org/docs/current/static/datatype-character.html
You should use TEXT data type for this use-case IMO.
https://www.postgresql.org/docs/9.1/datatype-character.html
Related
For example, I have a column of varchar(2000) for messages.
If most of my messages have a length of 50 char, the "real place in memory" occupied is optimized?
Or each of them occupies 2000 char?
I use PostgreSQL
The storage (and memory) space needed only depends on the actual data stored in the column. A column defined as varchar(2000) that only contains at most 50 characters, does not need more storage or memory than a column defined as varchar(50)
Quote from the manual
If the string to be stored is shorter than the declared length, [...] values of type character varying will simply store the shorter string
(Emphasis mine)
Note that this is different for the character data type - but that shouldn't be used anyway
I just would like to know if it is possible to limit character length with byte size for Postgres.
It would be very appreciated if you would tell me that.
Postgres version: 9.2.17
The length limit for a varchar column is in characters based on the encoding of the database. Unless you want to change your database to use a single-byte encoding (which I would strongly discourage), there is no direct way to do this.
What you can do is to use a check constraint that converts the character value to a byte array based on a specific encoding and then checks the length of the array:
alter table the_table
add constraint check_byte_length
check ( length(convert_to(the_column, 'UTF-8')) <= 42 )
I'm working with PostgreSQL 9.3.
I have a table with a varchar column that I always want to be filled with lowercase strings.
I could use the Postgres lower function before saving my values, but is there instead a way to define this column as a lowercase column?
You can accomplish this with a simple check in the column:
create table lower_field (
field1 varchar check (field1 = lower(field1))
);
What attribute of column I should use in order to get index value from postgresql sequence? valueNumeric? valueComputed?
As far as I understand the value of attribute should be nextval( 'simple_id_seq' ).
In postgresql sequence values are created as INTEGER or BIGINT.
Often this was done by using SERIAL or BIGSERIAL as column type ... but will indirectly create a sequencer of int or bigint and set the default value of the column to nextval(sequencer).
In a resultset of table data the column contains int or bigint.
Normaly there is no need to use nextval(sequencer) ... it fills the column on INSERT automatically (in the INSERT statemant the column shoult not appear).
Refer to http://www.postgresql.org/docs/9.3/static/datatype-numeric.html
If you do not want to use SERIAL or BIGSERIAL as suggested by #double_word_distruptor, use valueComputed.
With valueComputed you are telling Liquibase you are passing a function like nextval('simple_id_seq') and it will not try to parse it as a number or do any quoting.
You may also be able to use valueSequenceNext="simple_id_seq" to gain a little cross-database compatibility.
I need to increase the size of a character varying(60) field in a postgres database table without data loss.
I have this command
alter table client_details alter column name set character varying(200);
will this command increase the the field size from 60 to 200 without data loss?
The correct query to change the data type limit of the particular column:
ALTER TABLE client_details ALTER COLUMN name TYPE character varying(200);
Referring to this documentation, there would be no data loss, alter column only casts old data to new data so a cast between character data should be fine. But I don't think your syntax is correct, see the documentation I mentioned earlier. I think you should be using this syntax :
ALTER [ COLUMN ] column TYPE type [
USING expression ]
And as a note, wouldn't it be easier to just create a table, populate it and test :)
Yes. But it will rewrite this table and lock it exclusively for duration of rewriting — any query trying to access this table will wait until rewrite finishes.
Consider changing type to text and using check constraint for limiting size — changing constraint would not rewrite or lock a table.
you can use this below sql command
ALTER TABLE client_details
ALTER COLUMN name TYPE varchar(200)
From PostgreSQL 9.2 Relase Notes E.15.3.4.2
Increasing the length limit for a varchar or varbit column, or removing the limit altogether, no longer requires a table rewrite.
Changing the Column Size in Postgresql 9.1 version
During the Column chainging the varchar size to higher values, table re write is required during this lock will be held on table and user table not able access
till table re-write is done.
Table Name :- userdata
Column Name:- acc_no
ALTER TABLE userdata ALTER COLUMN acc_no TYPE varchar(250);