Database Reference
In-Depth Information
Most functions return null values when passed a null value.
NULL can be tested for using the IS [ NOT ] NULL conditional
operator.
An expression containing a null value always returns a null value.
The NVL (value, replace) function replaces null values in expressions,
avoiding SQL errors. The SET NULL environment variable does the
same thing in SQL*Plus.
Null values sort as the highest value by default.
4.3.6
Using Pseudocolumns
One or two simple examples will suffice with respect to the SELECT state-
ment. For example, the following query finds the ROWID (logical row
pointer) and ROWNUM (returned row number in current query) for each
row in the query. The result is shown in Figure 4.18.
SELECT ROWNUM, NAME, ROWID FROM ARTIST;
Figure 4.18
Using
Pseudocolumns.
That is the basics of the SELECT statement, plus a few other small bits
and pieces. Subsequent chapters will cover many of the details introduced
