UNNEST returns a table that contains one, two, or three columns. The first output column corresponds to the optional key value, if it was specified. The next output column has the same data type as the element type of the ARRAY type that was passed in. If the optional WITH ORDINALITY clause was specified, then UNNEST generates an additional integer column that contains the position associated with each element.
The table is populated with one row for each element of the ARRAY value passed to UNNEST. For an n-D ARRAY input value, the column containing the element values from the input n-D ARRAY are output in row-major order.