Jessica Richard wrote:
> I am tuning a database created by someone else.
> I noticed that some column lengths were defined longer than needed.
> For example, an Id column is holding a stand length of 20 characters but
> was defined as varchar(255).
> On some other columns, for example, a Description column is supposed to
> hold less than 100 characters but defined as text.
> I am trying to understand the performance impact if a column is over
> defined in the following cases:
> 1. char(20) vs varchar(20)
> 2. varchar(20) vs varchar(255)
> 3. varchar(255) vs text
Interestingly, the Postgres documentation has the answer:
> Tip: There are no performance differences between these three types, apart
> from increased storage size when using the blank-padded type, and a few extra
> cycles to check the length when storing into a length-constrained column.
> While character(n) has performance advantages in some other database systems,
> it has no such advantages in PostgreSQL. In most situations text or character
> varying should be used instead.
Performance is not the only issue. The semantics of CHAR and VARCHAR differ.
You cannot use them equivalently.
I recommend searching the docs as a first approach to finding such answers.
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