Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 12
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Datatypes
Choosing the right datatype seems so easy and straightforward, but many times I see it
done incorrectly. The most basic decision—what type you use to store your data in—will have
repercussions on your applications and data for years to come. Choosing the appropriate
datatype is paramount and hard to change after the fact—that is, once you implement it you
might be stuck with it for quite a while.
In this chapter, we’ll take a look at all of the Oracle basic datatypes available and discuss
how they are implemented and when each might be appropriate to use. We won’t examine
user-defined datatypes, as they’re simply compound objects derived from the built-in Oracle
datatypes. We’ll investigate what happens when you use the wrong datatype for the job, or
even just the wrong parameters to the datatype (length, precision, scale, and so on). By the
end of this chapter, you’ll have an understanding of the types available to you, how they’re
implemented, when to use each type and, as important, why using the right type for the job
is key.
An Overview of Oracle Datatypes
Oracle provides 22 different SQL data types for us to use. Briefly, they are as follows:
• CHAR: A fixed-length character string that will be blank padded with spaces to its maximum
length. A non-null CHAR(10) will always contain 10 bytes of information using the
default National Language Support (NLS) settings. We will cover NLS implications in
more detail shortly. A CHAR field may store up to 2,000 bytes of information.
• NCHAR: A fixed-length character string that contains UNICODE formatted data. Unicode is
a character-encoding standard developed by the Unicode Consortium with the aim of
providing a universal way of encoding characters of any language, regardless of the
computer system or platform being used. The NCHAR type allows a database to contain
data in two different character sets: the CHAR type and NCHAR type use the database’s
character set and the national character set, respectively. A non-null NCHAR(10) will
always contain 10 characters of information (note that it differs from the CHAR type in
this respect). An NCHAR field may store up to 2,000 bytes of information.
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