There is no difference, under the hood it’s all
varlena (variable length array).
Check this article from Depesz: http://www.depesz.com/index.php/2010/03/02/charx-vs-varcharx-vs-varchar-vs-text/
A couple of highlights:
To sum it all up:
- char(n) – takes too much space when dealing with values shorter than
n(pads them to
n), and can lead to subtle errors because of adding trailing
spaces, plus it is problematic to change the limit
- varchar(n) – it’s problematic to change the limit in live environment (requires exclusive lock while altering table)
- varchar – just like text
- text – for me a winner – over (n) data types because it lacks their problems, and over varchar – because it has distinct name
The article does detailed testing to show that the performance of inserts and selects for all 4 data types are similar. It also takes a detailed look at alternate ways on constraining the length when needed. Function based constraints or domains provide the advantage of instant increase of the length constraint, and on the basis that decreasing a string length constraint is rare, depesz concludes that one of them is usually the best choice for a length limit.