Tom Lane wrote: > Simon Riggs <[EMAIL PROTECTED]> 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:
... > b) If VB is 0 (zero) and VE is negative, then an exception condition is > raised: data exception ? invalid argument for power function. Well, this indicates we shouldn't return "zero raised to a negative power is undefined", but rather the power error we are giving now, or are you saying we should return the "power" error code but an error message mentioning zero? > c) If VB is 0 (zero) and VE is 0 (zero), then the result is 1 (one). I have updated the C comments to mention the spec also requires we return 1 in this case. C comment updated attached and applied. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
Index: src/backend/utils/adt/float.c =================================================================== RCS file: /cvsroot/pgsql/src/backend/utils/adt/float.c,v retrieving revision 1.155 diff -c -c -r1.155 float.c *** src/backend/utils/adt/float.c 21 Apr 2008 00:26:45 -0000 1.155 --- src/backend/utils/adt/float.c 9 May 2008 15:34:53 -0000 *************** *** 1331,1337 **** /* * The SQL spec requires that we emit a particular SQLSTATE error code for ! * certain error conditions. */ if ((arg1 == 0 && arg2 < 0) || (arg1 < 0 && floor(arg2) != arg2)) --- 1331,1338 ---- /* * The SQL spec requires that we emit a particular SQLSTATE error code for ! * certain error conditions. Specifically, we don't return a divide-by-zero ! * error code for 0 ^ -1. */ if ((arg1 == 0 && arg2 < 0) || (arg1 < 0 && floor(arg2) != arg2)) Index: src/backend/utils/adt/numeric.c =================================================================== RCS file: /cvsroot/pgsql/src/backend/utils/adt/numeric.c,v retrieving revision 1.112 diff -c -c -r1.112 numeric.c *** src/backend/utils/adt/numeric.c 8 May 2008 22:17:54 -0000 1.112 --- src/backend/utils/adt/numeric.c 9 May 2008 15:34:53 -0000 *************** *** 1893,1900 **** trunc_var(&arg2_trunc, 0); /* ! * Return special SQLSTATE error codes for a few conditions mandated by ! * the standard. */ if ((cmp_var(&arg1, &const_zero) == 0 && cmp_var(&arg2, &const_zero) < 0) || --- 1893,1901 ---- trunc_var(&arg2_trunc, 0); /* ! * The SQL spec requires that we emit a particular SQLSTATE error code for ! * certain error conditions. Specifically, we don't return a divide-by-zero ! * error code for 0 ^ -1. */ if ((cmp_var(&arg1, &const_zero) == 0 && cmp_var(&arg2, &const_zero) < 0) || *************** *** 5283,5288 **** --- 5284,5290 ---- /* * While 0 ^ 0 can be either 1 or indeterminate (error), we * treat it as 1 because most programming languages do this. + * SQL:2003 also requires a return value of 1. * http://en.wikipedia.org/wiki/Exponentiation#Zero_to_the_zero_power */ set_var_from_var(&const_one, result);
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