The ARRAY concatenation operator for one-dimensional (1-D) ARRAY data types is partially ANSI SQL:2011 compliant.
The ARRAY concatenation operator requires that both operands are instances of the same ARRAY type and that the target type of the concatenation operation is also the same type. This is a deviation from the ANSI standard because it defines the target data type of a 1-D ARRAY concatenation to be a new 1-D ARRAY type with the length defined as the sum of the length of both operands.