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Re: pgsql: Have numeric 0 ^ 4.3 return 1, rather than an error, and have 0 ^

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-committers(at)postgresql(dot)org
Subject: Re: pgsql: Have numeric 0 ^ 4.3 return 1, rather than an error, and have 0 ^
Date: 2008-05-09 14:37:07
Message-ID: 13701.1210343827@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-committers
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> Wikipedia says that exponentiation of zero to a negative power implies
> division by zero, so shouldn't we throw a "division by zero" error?

I think it should be a specific message like "zero raised to a negative
power is undefined".  It's not like it's going to take us any extra code
to know that we are faced with that case.

BTW, I realized that SQL:2003 spells it all out for us in explicit
detail:

12)If <power function> is specified, then let NVEB be the <numeric value
expression base>, then let VB be the value of NVEB, let NVEE be the
<numeric value expression exponent>, and let VE be the value of NVEE.

Case: 

a) If either VB or VE is the null value, then the result is the null value. 

b) If VB is 0 (zero) and VE is negative, then an exception condition is
raised: data exception  invalid argument for power function.

c) If VB is 0 (zero) and VE is 0 (zero), then the result is 1 (one). 

d) If VB is 0 (zero) and VE is positive, then the result is 0 (zero). 

e) If VB is negative and VE is not equal to an exact numeric value with
scale 0 (zero), then an exception condition is raised: data exception
 invalid argument for power function.

f) If VB is negative and VE is equal to an exact numeric value with
scale 0 (zero) that is an even number, then the result is the result of
	EXP(NVEE*LN(-NVEB)) 

g) If VB is negative and VE is equal to an exact numeric value with
scale 0 (zero) that is an odd number, then the result is the result of
	-EXP(NVEE*LN(-NVEB)) 

h) Otherwise, the result is the result of 
	EXP(NVEE*LN(NVEB)) 


			regards, tom lane

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