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SQL: [Docs] Add example for custom bucketing with CASE #41787

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SQL: [Docs] Add example for custom bucketing with CASE #41787

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SQL: [Docs] Add example for custom bucketing with CASE
matriv May 3, 2019
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matriv May 6, 2019
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matriv May 6, 2019
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25 changes: 25 additions & 0 deletions docs/reference/sql/functions/conditional.asciidoc
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Expand Up @@ -98,6 +98,31 @@ an error message would be returned, mentioning that *'foo'* is of data type *key
which does not match the expected data type *integer* (based on result *10*).
===============================

[[sql-functions-conditional-case-groupby-custom-buckets]]
[TIP]
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I would remove the TIP header and promote this to a section (=====) - I think it's big enough to warrant a proper entry.

===============================
CASE can be used as a GROUP BY key in a query to facilitate custom bucketing
and assign descriptive names to those buckets. If for example the number of
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If, for example, the number....

values for a key are too many or, simply, ranges of those values are more
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the number ..... is too large. values.... are too many

interesting than every single value, CASE can create custom buckets as in the
following example:

[source, sql]
SELECT count(*) AS count,
CASE WHEN NVL(languages, 0) = 0 THEN 'zero'
WHEN languages = 1 THEN 'one'
WHEN languages = 2 THEN 'bilingual'
WHEN languages = 3 THEN 'trilingual'
ELSE 'multilingual'
END as lang_skills
FROM employees
GROUP BY lang_skills
ORDER BY lang_skills;

With this query, we can create normal grouping buckets for values _0, 1, 2, 3_ with
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With this query, one can create

descriptive names, and every value _>= 4_ falls into the _multilingual_ bucket.
===============================

[[sql-functions-conditional-coalesce]]
==== `COALESCE`

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4 changes: 4 additions & 0 deletions docs/reference/sql/language/syntax/commands/select.asciidoc
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Expand Up @@ -204,6 +204,10 @@ Multiple aggregates used:
include-tagged::{sql-specs}/docs/docs.csv-spec[groupByAndMultipleAggs]
----

[TIP]
If custom bucketing is required, it can be achieved with the use of `<<sql-functions-conditional-case, CASE>>`,
as shown <<sql-functions-conditional-case-groupby-custom-buckets, here>>.

[[sql-syntax-group-by-implicit]]
===== Implicit Grouping

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