Database Reference
In-Depth Information
14
Expressions
In this chapter:
How can expressions be classified?
What are regular expressions?
What is the Oracle Expression Filter?
There are three distinct parts to this chapter. The first part covers details
of expressions in Oracle, which are covered more or less throughout this
topic. This chapter attempts to simply break things into logical parts. The
second part of this chapter deals with regular expressions catering for text
pattern matching and searching. The third part briefly covers the Oracle
Expression Filter.
A fundamental but often difficult to answer question is this: What is an
expression? There is a simple explanation. Anything resulting in a value is
an expression. An expression can consist of a single scalar value or a highly
complex formula. Here are some example expressions:
1 is an expression.
x + y is an expression.
2
mc
is an expression.
The subquery (highlighted) in the following query is a list of expressions:
SELECT * FROM COUNTRY WHERE CONTINENT_ID IN
(SELECT CONTINENT_ID FROM CONTINENT)
;
