Update user_guide_src/source/database/query_builder.rst

Clarification for unionAll() method.

Co-authored-by: Michal Sniatala <michal@sniatala.pl>

Author: iRedds

user_guide_src/source/database/query_builder.rst

@@ -712,7 +712,7 @@ In the example below, we get the first 5 users + the last 5 users and sort the r
 $builder->unionAll()
 --------------------
 
-The behavior is the same as the ``union()`` method.
+The behavior is the same as the ``union()`` method. However, all results will be returned, not just the unique ones.
 
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 Query grouping