Thanks for the explanation and examples!
Zev
On 11/28/2013 10:03 AM, Tom Lane wrote:
David Johnston <polobo@xxxxxxxxx> writes:
Zev Benjamin wrote
It appears that unnest, when called on a multi-dimensional array,
effectively flattens the array first. For example: ...
Multidimensional arrays do have shortcomings in the current implementation
of which this is one. I'm not sure, though, if there is anything
substantial and centralized in the docs so pertaining.
It might be worth explaining that this is a consequence of the fact that
Postgres treats all arrays over the same element type as being of the
same data type --- that is, 1-D and 2-D arrays are not distinguished
by the type system. Thus, when the polymorphic function "unnest(anyarray)
returns setof anyelement" is applied to an integer array, it must return
a series of integers; not a series of lower-dimensional arrays.
There have been some discussions over whether this could be changed
without a backwards-compatibility disaster, but nobody sees how.
regards, tom lane
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