How to get the dimensionality of an ARRAY column?

Question

I\'m working on a project that collects information about your schema from the database directly. I can get the data_type of the column using information_sche

Answer 1

For starters, the dimensionality of an array is not reflected in the data type in Postgres. The syntax integer[][] is tolerated, but it's really just integer[] internally.
Read the manual here.

This means, that dimensions can vary within the same data type (the same table column).

To get actual dimensions of a particular array value:

SELECT array_dims(my_arr);  -- [1:2][1:3]

Or to just get the number of dimensions:

SELECT array_ndims(my_arr);  -- 2

There are more array functions for similar needs. See table of array functions in the manual.

Related:

• Use string[][] with ngpsql

If you need to enforce particular dimensions in a column, add a CHECK constraint. To enforce 2-dimensional arrays:

ALTER TABLE tbl ADD CONSTRAINT tbl_arr_col_must_have_2_dims
CHECK (array_ndims(arr_col) = 2);