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[8.16] ESQL: Docs: COUNT: add an explanation to the use of the 3VL (#116684) #117005

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Nov 19, 2024
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[8.16] ESQL: Docs: COUNT: add an explanation to the use of the 3VL (#116684) #117005

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2 changes: 1 addition & 1 deletion docs/reference/esql/functions/examples/count.asciidoc
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4 changes: 3 additions & 1 deletion .../esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/aggregate/Count.java
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,9 @@ public class Count extends AggregateFunction implements ToAggregator, SurrogateE
),
@Example(
description = "To count the same stream of data based on two different expressions "
+ "use the pattern `COUNT(<expression> OR NULL)`",
+ "use the pattern `COUNT(<expression> OR NULL)`. This builds on the three-valued logic "
+ "({wikipedia}/Three-valued_logic[3VL]) of the language: `TRUE OR NULL` is `TRUE`, but `FALSE OR NULL` is `NULL`, "
+ "plus the way COUNT handles `NULL`s: `COUNT(TRUE)` and `COUNT(FALSE)` are both 1, but `COUNT(NULL)` is 0.",
file = "stats",
tag = "count-or-null"
) }
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