PostgreSQL equivalent to SQL Server NVARCHAR (MAX)

Question

我知道在 PostgreSQL 中， VARCHAR(n)等效于 SQL Server 的NVARCHAR(n) ，但是我如何在 PostgreSQL 中使用类似于VARCHAR(MAX)东西，类似于 SQL Server 中的NVARCHAR(MAX)东西？

Answer 1

In PostgreSQL for char(n) and varchar(n) it is just limited by n argument (not sure about nature of such limitation, it seems that it is 20 Mb or 10M of 2-bytes characters or something):

postgres=# select 'a'::varchar(999999999);
ERROR:  length for type varchar cannot exceed 10485760

So if you really need the equivalent for MS SQL Server nvarchar(max) - it could be varchar(10485760)

However to use really unlimited character values there are two ways: varchar or character varying without argument or just text type. Read more in thedocumentation and note about Tip provided in it:

There is no performance difference among these three types, apart from increased storage space when using the blank-padded type, and a few extra CPU cycles to check the length when storing into a length-constrained column. While character(n) has performance advantages in some other database systems, there is no such advantage in PostgreSQL; in fact character(n) is usually the slowest of the three because of its additional storage costs. In most situations text or character varying should be used instead.

Answer 2

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

Answer 3

text, varchar can be used for this requirement. i used varchar

Character Types Description

character varying(n), varchar(n) --- variable-length with limit

character(n), char(n) -- fixed-length, blank padded

text, varchar -- variable unlimited length

More Details: https://www.postgresqltutorial.com/postgresql-char-varchar-text/