Aggregate Functions (Counting Distinct Values) , Window Functions (Semi-structured Data Aggregation)
Returns an ARRAY that contains the union of the distinct values from the input ARRAYs in a column. You can use this to aggregate distinct values in ARRAYs produced by ARRAY_UNIQUE_AGG.
ARRAY_UNION_AGG( <column> )
The column containing the ARRAYs with the distinct values (the ARRAYs produced by ARRAY_UNIQUE_AGG).
The function returns an ARRAY containing the distinct values from the ARRAYs in
column. The values in the ARRAY are in
no particular order, and the order is not deterministic.
Note that this function uses multiset semantics, which means that the maximum number of occurrences of an individual value in a single input ARRAY determines the number of occurrences of that value in the output ARRAY. See Examples.
The function ignores NULL values in
column and in the ARRAYs in
column contains only
NULL values or the table containing
column is empty, the function returns an empty ARRAY.
This function can be used as either of the following types of functions:
When used as a window function, this does not support window frames.
Aggregation: Union of Arrays¶
The following example illustrates how the function returns the union of distinct values from two ARRAYs:
CREATE TABLE union_test(a array); INSERT INTO union_test SELECT PARSE_JSON('[ 1, 1, 2]') UNION ALL SELECT PARSE_JSON('[ 1, 2, 3]'); SELECT ARRAY_UNION_AGG(a) FROM union_test; +-------------------------+ | ARRAY_UNION_AGG(A) | +-------------------------+ | [ 1, 1, 2, 3] | +-------------------------+
The operation uses multiset semantics. The value
1 appears twice in the output
because it appears twice in one of the input arrays.
See Using Arrays to Compute Distinct Values for Hierarchical Aggregations.