GRAYLOG - Chapter 7, Exercise 1 Solution
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Correctly Parenthesizing a Mixed AND/OR Query

PROBLEM
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A query needs to match either service scout or service search, but only
at critical or error level (2 or 3). Using this chapter's own real
parenthesization rule, write it correctly.

SOLUTION
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This chapter established that mixing AND and OR without explicit
grouping is genuinely ambiguous, and that Lucene's own documentation
recommends always parenthesizing each logical group separately.

Two real groups are needed here:
  1. Either service - grouped with OR: (service:scout OR service:search)
  2. Level restricted to critical/error - grouped with OR:
     level:(2 OR 3), per Chapter 3's own syntax

Combining both groups with AND:

    (service:scout OR service:search) AND level:(2 OR 3)

ANSWER: (service:scout OR service:search) AND level:(2 OR 3)

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WHY THIS WORKS AS AN ANSWER

This directly applies the chapter's own real worked example -
(jakarta OR apache) AND website - substituting this course's own real
field values in the same structural shape. Without the outer
parentheses around the two service values, the query's own real meaning
would become genuinely ambiguous, exactly the trap this chapter's own
warn-box described.