"Itagaki Takahiro" <itagaki(dot)takahiro(at)gmail(dot)com> writes:
> For query concat_ws('/', NULL, 'X'),
> PostgreSQL 9.1 returns '/X', but MySQL returns 'X'.
> I think postgres should return 'X' because of compatibility.
> Another reason is that both of the two queries below return 'X'.
> - concat_ws('/', 'X', NULL)
> - array_to_string(ARRAY[NULL, 'X'], '/')
Yeah, I think you're right. Fortunately it's not too late to change
this without introducing backwards-compatibility issues of our own.
Will fix.
regards, tom lane