CODEWITHSUNDEEP
arrayspostgresql
David Macek
David Macek

Reputation: 927

Why does `array_ndims(array[])` produce NULL?

I'm trying to test for an empty array. I understand the reasoning behind array_length returing NULL since it's a 0-dimensional array, but why is array_ndims(array[]::int array) not 0, but rather NULL?

Upvotes: 1

Views: 138

Answers (1)

Łukasz Kamiński
Łukasz Kamiński

Reputation: 5950

Looks like it will never return 0:

/* Sanity check: does it look like an array at all? */
    if (AARR_NDIM(v) <= 0 || AARR_NDIM(v) > MAXDIM)
        PG_RETURN_NULL();

You could write your own C function for this, simply change <= 0 into < 0. As for reasoning behind this, I can't find anything.

Source is in: https://www.postgresql.org/ftp/source/v10.1/ (same thing for 9.6.2, with is what I checked initially)

File: ./src/backend/utils/adt/arrayfuncs.c

Look for simple, 10 line function: array_ndims

Upvotes: 1

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