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

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CHAPTER 12 ■ DATATYPES
TABLE_OWN TABLE PARTIT HIGH_VALUE
--------- ----- ------ ------------------------------
OPS$TKYTE T PART1 TO_DATE(' 2003-03-13 00:00:00'
, 'SYYYY-MM-DD HH24:MI:SS', 'N
LS_CALENDAR=GREGORIAN')
OPS$TKYTE T
PART2 TO_DATE(' 2003-03-14 00:00:00'
, 'SYYYY-MM-DD HH24:MI:SS', 'N
LS_CALENDAR=GREGORIAN')
Using this same technique—that of processing the result of a query that returns a single
row with a single LONG column in a function—you can implement your own INSTR, LIKE, and so
on as needed.
This implementation works well on the LONG type, but it will not work on LONG RAW types.
LONG RAWs are not piecewise accessible (there is no COLUMN_VALUE_LONG_RAW function in DBMS_SQL).
Fortunately, this is not too serious of a restriction since LONG RAWs are not used in the dictionary
and the need to “substring” so you can search on it is rare. If you do have a need to do so,
however, you will not use PL/SQL unless the LONG RAW is 32KB or less, as there is simply no
method for dealing with LONG RAWs over 32KB in PL/SQL itself. Java, C, C++, Visual Basic, or
some other language would have to be used.
Another approach is to temporarily convert the LONG or LONG RAW into a CLOB or BLOB using
the TO_LOB built-in function and a global temporary table. Your PL/SQL procedure could be as
follows:
Insert into global_temp_table ( blob_column )
select to_lob(long_raw_column) from t where...
This would work well in an application that occasionally needs to work with a single
LONG RAW value. You would not want to continuously do that, however, due to the amount of
work involved. If you find yourself needing to resort to this technique frequently, you should
definitely convert the LONG RAW to a BLOB once and be done with it.
DATE, TIMESTAMP, and INTERVAL Types
The native Oracle datatypes of DATE, TIMESTAMP, and INTERVAL are closely related. The DATE and
TIMESTAMP types store fixed date/times with varying degrees of precision. The INTERVAL type is
used to store an amount of time, such as “8 hours” or “30 days,” easily. The result of subtracting
two dates might be an interval; for example, the result of adding an interval of 8 hours to a
TIMESTAMP results in a new TIMESTAMP that is 8 hours later.
The DATE datatype has been part of Oracle for many releases—as far back as my experience
with Oracle goes, which means at least back to version 5 and probably before. The TIMESTAMP
and INTERVAL types are relative newcomers to the scene by comparison, as they were introduced
with Oracle9i Release 1. For this simple reason, you will find the DATE datatype to be the
most prevalent type for storing date/time information. But many new applications are using
the TIMESTAMP type for two reasons: it has support for fractions of seconds, while the DATE type
does not; and it has support for time zones, something the DATE type also does not have.
We’ll take a look at each type after discussing DATE/TIMESTAMP formats and their uses.