Handling NULL sets within the SQL CASE statement

Home
E-mail Us
Oracle Articles
New Oracle Articles

Oracle Training
Oracle Tips
Oracle Forum
Class Catalog

Remote DBA
Oracle Tuning
Emergency 911
RAC Support
Apps Support
Analysis
Design
Implementation
Oracle Support

SQL Tuning
Security
Oracle UNIX
Oracle Linux
Monitoring
Remote support
Remote plans
Remote services
Application Server
Applications
Oracle Forms
Oracle Portal
App Upgrades
SQL Server
Oracle Concepts
Software Support
Remote Support
Development
Implementation

Consulting Staff
Consulting Prices
Help Wanted!

Oracle Posters
Oracle Books
Oracle Scripts
Ion
Excel-DB

Don Burleson Blog

Handling NULL sets within the SQL CASE statement

Oracle Database Tips by Donald BurlesonNovember 7, 2015

Question: I'm trying to write a case statement that will query the maximum date from a table, and if the result is null- return sysdate.

select max(case somedate when NULL then sysdate
else somedate
end) somedate
from trydates
where somedate < (sysdate-4)

will return max(somedate) even if the condition returns no results (when the condition is: somedate < sysdate-40, there is no matching value and I get ' ' as a result). Is there a way I can catch that NULL returned when there is no date returned by the condition at the end? My original statement was using decode function:

SELECT
   DECODE(MAX(somedate),
   NULL, sysdate, MAX(somedate))
FROM trydates
WHERE
   somedate BETWEEN :lower_active_bound AND :from_date

Answer: Oracle CASE SQL allows you to add "Boolean logic" and branching using the decode and CASE clauses. The case statement is a more flexible extension of the Decode statement. In its simplest form the Oracle CASE function is used to return a value when a match is found, it it's trickier to handle a NULL condition from a subquery.

Laurent Schneider provides this answer:

select max(case somedate when NULL then sysdate
else somedate
end) somedate
from trydates
where somedate < (sysdate-4)
   having
      max(
         case when somedate when NULL then sysdate
         else somedate
      end) IS NOT NULL

If you like Oracle tuning, you might enjoy my book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

��