BUG #14521: pg_attribute.attndims = 0 for array column

krzysztof.heim@gmail.com writes:

I have base table A with column type integer array.
I also have table B derived from table A.

When I query pg_attribute for table A, attndims shows 1 (correct), when I do
same query for table B - attndims shows 0 for same column.

Is it a bug, or it's desired behavior (since it's a derived column).

We don't really care. attndims is a historical leftover and should never
be relied on for any semantically significant purpose.

TBH, my inclination would be to remove the column altogether rather than
"fix" this.

regards, tom lane

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Krzysztof Heim <krzysztof.heim@gmail.com> writes:

If I may ask, what is then the best way of checking if column is array.

The standard way for C code is to use this macro from lsyscache.h:

#define type_is_array(typid) (get_element_type(typid) != InvalidOid)

or depending on what you're doing, you might want these semantics:

/* type_is_array_domain accepts both plain arrays and domains over arrays */
#define type_is_array_domain(typid) (get_base_element_type(typid) != InvalidOid)

or then again, you might just want to check if the type has nonzero
typelem --- that would be the appropriate thing if you want to see
whether the type is subscriptable.

regards, tom lane

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