In the searched case every case has its own expression. This can for instance be helpful when using ranges. The else clause is optional. NULL values are one of the most mind-boggling values in the Oracle database. Find out more. Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed.
View all articles by Patrick Barel. FROM emp t. WHERE t. NVL expr1 , expr2. NVL2 expr1 , expr2 , expr3. LNNVL condition. FROM emp e. This is the flavor of db2 a lot of people see. Show 1 more comment. Doug Currie Doug Currie Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. Featured on Meta.
Nick that the NULL values in his spouse and status columns represent an unknown value. To maintain the integrity of a database, both interpretations of NULL are necessary. Binary logic uses two values: True and False, 0 and 1, etc. Ternary logic uses three values. Interesting, but not something you need to memorize. As you will see, SQL helps us work around this tricky logic. Which is handy, because SQL comparison operations use the same ternary logic.
Whatever the comparison column contains — salaries, pet names, etc. This is true even if the column value is NULL. This is what confuses programmers who are experienced in other languages. So as our query is evaluated, it is going to look like this:. This comparison is also going to return unknown. We can see from the truth table earlier that NOT unknown is going to return unknown. Also - Oracle would now have to be concerned with all the possible data combinations that developers could be throwing at it - while currently they are well aware of exactly how it is being used.
So - just because it is not documented does not mean it is not doing an excellent job at the internal function. However - likewise - just because it is doing an excellent job at the internal function - does not necessarily mean it will work well for you in your development now - or in the future. On the other hand - if you test well - are confident of the data you are sending to it falls well within your test cases and you are planning on retesting when the Oracle binaries change - perhaps it is reasonable to decide if this is a risk level you are comfortable with.
Biggest thing is to be sure you are making a well informed decision. Fair points Tim, PA, wouldn't disagree with you on those or Tom's.
Re Oracle's use of them with MV fast refreshes: they're used with MERGE operations, on the criteria matching specifically, and that's where I would consider using them myself, with appropriate circumspection!
Appreciate your valuable advice as always. Thanks, Priya. September 26, - am UTC. Isnt null! TIA PinguSan. But the second Zero-Length String compare does not make sense to me. The third case makes sense to me. August 14, - am UTC. Zero length strings I know what the answer to my question is A reader, April 10, - pm UTC. April 11, - am UTC. My favorite elegant way xelay, June 18, - am UTC. The shortest way i prefer to use is: if a '!
Also is this the correct approach for comparing NULLable values. November 01, - pm UTC. Be careful with '! Falco, April 09, - am UTC.
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