On Sat, Jan 21, 2017 at 9:39 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Pavan Deolasee <pavan.deola...@gmail.com> writes: > > On Sat, Jan 21, 2017 at 9:09 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> Hm, but what of the "null" value? Also, I get > >> > >> $ perl -e 'use warnings; use Test::More; ok("2017-01-01" != "null", > "ok");' > >> Argument "null" isn't numeric in numeric ne (!=) at -e line 1. > >> Argument "2017-01-01" isn't numeric in numeric ne (!=) at -e line 1. > >> ok 1 - ok > > > It declares the test as "passed", right? > > Oh! So it does. That is one darn weird behavior of the != operator. > > Indeed! See this: # first numeric matches, doesn't check beyond that $ perl -e 'if ("2017-23" != "2017-24") {print "Not equal\n"} else {print "Equal\n"}' Equal # first numeric doesn't match, operators works ok $ perl -e 'if ("2017-23" != "2018-24") {print "Not equal\n"} else {print "Equal\n"}' Not equal # comparison of numeric with non-numeric, works ok $ perl -e 'if ("2017-23" != "Foo") {print "Not equal\n"} else {print "Equal\n"}' Not equal # numeric on RHS, works ok $ perl -e 'if ("Foo" != "2018-24") {print "Not equal\n"} else {print "Equal\n"}' Not equal These tests show that the operator returns the correct result it finds a numeric value at the start of the string, either on LHS or RHS. Also, it will only compare the numeric values until first non-numeric character is found. # no numeric on either side $ perl -e 'if ("Fri 2017-23" != "Fri 2017-23") {print "Not equal\n"} else {print "Equal\n"}' Equal *# no numeric on either side, arbitrary strings declared as equal* $ perl -e 'if ("Fri 2017-23" != "Foo") {print "Not equal\n"} else {print "Equal\n"}' Equal These two tests show why we saw no failure earlier. If neither LHS or RHS string has a starting numeric value, the operator declares the arguments as equal, irrespective of their values. I tested the same with == operator and that also exhibits the same behaviour. Weird and I wonder how it's not a source of constant bugs in perl code (I don't use perl a lot, so may be those who do are used to either turning warnings on or know this already. > > > There's still the point that we're not actually exercising this script > in the buildfarm ... > Yes indeed. Thanks, Pavan -- Pavan Deolasee http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services