Use the set_union function in APL to combine two dynamic arrays into one, returning a new array that includes all distinct elements from both. The order of elements in the result is not guaranteed and may differ from the original input arrays. You can use set_union when you need to merge two arrays and eliminate duplicates. It is especially useful in scenarios where you need to perform set-based logic, such as comparing user activity across multiple sources, correlating IPs from different datasets, or combining traces or log attributes from different events.

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For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.
APL’s set_union works similarly to using mvappend followed by mvdedup in SPL. While SPL stores multivalue fields and uses field-based manipulation, APL focuses on dynamic arrays. You need to explicitly apply set logic in APL using functions like set_union.
| eval result=mvappend(array1, array2)
| eval result=mvdedup(result)
Standard SQL doesn’t support arrays as first-class types or set functions like set_union. However, conceptually, set_union behaves like applying UNION between two subqueries that return one column each, followed by a DISTINCT.
SELECT value FROM (
  SELECT value FROM table1
  UNION
  SELECT value FROM table2
)

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Usage

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Syntax

set_union(Array1, Array2)

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Parameters

NameTypeDescription
Array1dynamicThe first array to merge.
Array2dynamicThe second array to merge.

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Returns

A dynamic array that contains the distinct elements of both input arrays.

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Example

Use set_union to return the union of two arrays. Query 
['sample-http-logs']
| extend together = set_union(dynamic([1, 2, 3]), dynamic([2, 3, 4, 5]))
Run in Playground Output
_timetogether
May 22, 11:42:52[1, 2, 3, 4, 5 ]
  • set_difference: Returns elements in the first array that are not in the second. Use it to find exclusions.
  • set_has_element: Tests whether a set contains a specific value. Prefer it when you only need a Boolean result.
  • set_union: Returns the union of two or more sets. Use it when you need any element that appears in at least one set instead of every set.