Final answer:
COLLECT_SET is a function that creates an array of unique values without duplicates, while FLATTEN transforms nested array structures into a single-layered, one-dimensional array. COLLECT_SET is for uniqueness, whereas FLATTEN is for simplification of data structures.
Step-by-step explanation:
The difference between COLLECT_SET and FLATTEN with respect to arrays lies in their functionality. COLLECT_SET is a function used in data processing which gathers unique elements from multiple records and combines them into a single array without any duplicates. This ensures that even if the same value occurs in multiple records, it will only appear once in the resulting array. The main purpose of this function is to avoid redundancy and provide a set of distinct values from a larger dataset.
On the other hand, FLATTEN is used to transform a nested array structure into a single, one-dimensional array. When you have arrays within arrays, FLATTEN merges them into a single level, making it easier to process and analyze data. It essentially 'flattens' the layers of nested structures, hence the name. The primary goal of the FLATTEN function is to simplify complex array structures so that they can be more easily manipulated.
For example, if you have an array of arrays like [[1, 2], [3, 4], [1, 2]], using FLATTEN will result in [1, 2, 3, 4, 1, 2], whereas using COLLECT_SET would result in a set with unique values only, like [1, 2, 3, 4].