Searching for a more elegant way to write my where clause.

Question

Hi,
I have a table T which has two columns : X(Varchar2(100)), and Y(Varchar2(100)).I want to know all the rows in the table T for which two conditions are simultaneously true: the first condition is X is not null or Y is not null, and the second condition is not(X  is not null and Y is not null). So I write my query like below:
select *
from T
where (X is not null or Y is not null) and  not(X  is not null and Y is not null)But the way I formulate my where clause doesn't seem elegant to me. Please, could I obtain the same result with a more elegant where clause?
Thanks.

Answer 1

<font face="courier">
where (X is not null or Y is not null) and <font color="red">not(X is not null and Y is not null)</font><br>
<font color="red">De Morgan</font><br>
where ((X is not null) or (Y is not null)) and (<font color="red">not(X is not null) or not(Y is not null)</font>)<br><br>
where ((X is not null) or (Y is not null)) and (<b>not(X is not null)</b> or <b>not(Y is not null)</b>)<br>
<b>double negation</b><br>
where ((X is not null) or (Y is not null)) and (<b>(X is null)</b> or <b>(Y is null)</b>)<br><br>
where (<font color="green">(X is not null) <b>or</b> (Y is not null)</font>) <font color="blue"><b>and</b> ((X is null) or (Y is null))</font><br>
Distributivity of <font color="blue"><b>and</b></font> over <font color="green"><b>or</b></font><br>
where (<font color="green">(X is not null)</font> <font color="blue"><b>and</b> ((X is null) or (Y is null))</font>) <font color="green"><b>or</b></font> (<font color="green">(Y is not null)</font> <font color="blue"><b>and</b> ((X is null) or (Y is null))</font>)<br><br>
where (<font color="red">(X is not null) <b>and</b></font> <font color="magenta">((X is null) <b>or</b> (Y is null))</font>) or (<b>(Y is not null) and ((X is null) or (Y is null))</b>)<br>
Distributivity of <font color="red"><b>and</b></font> over <font color="magenta"><b>or</b></font> applied to the <b>second term</b> too<br>
where ((<font color="red">(X is not null) <b>and</b></font> <font color="magenta">(X is null)</font>) <font color="magenta"><b>or</b></font> (<font color="red">(X is not null) <b>and</b></font> <font color="magenta">(Y is null)</font>)) or <br>      ((<b>(Y is not null) and (X is null)</b>)<b> or </b>(<b>(Y is not null) and (Y is null)</b>))<br><br>
<font color="green"><b>Negation</b></font><br>
where ((<font color="green"><strike>(X is not null)</strike> <b>not(Y is null)</b></font> and (X is null)) or ((X is not null) and (Y is null))) or <br>      (((Y is not null) and (X is null)) or (<font color="green"><strike>(Y is not null)</strike> <b>not(Y is null)</b>)</font> and (Y is null)))<br><br>
where ((<font color="blue">not(X is null) and (X is null)</font>) or ((X is not null) and (Y is null))) or <br>      (((Y is not null) and (X is null)) or (<font color="blue">not(Y is null) and (Y is null)</font>))<br>
<font color="blue">Complementation</font><br>
where ((<font color="blue">false</font>) or ((X is not null) and (Y is null))) or <br>      (((Y is not null) and (X is null)) or (<font color="blue">false</font>))<br><br>
<b>where ((X is not null) and (Y is null)) or ((Y is not null) and (X is null))</b><br><br>
preferring clarity (in the eye of beholder as always) over efficiency<br><br>
<b>where x || y in (x,y)</b><br><br>
Regards
Etbin
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Edited by: Etbin on 28.8.2011 11:45
steps separated with empty lines, negation enhanced