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Distinctness
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
A useful thing to do when aggregating data is to remove duplicate input first, prior to aggregation. A few aggregate functions support a DISTINCT keyword for that purpose. For example, we can query
SELECT count(AUTHOR_ID), count(DISTINCT AUTHOR_ID), group_concat(AUTHOR_ID), group_concat(DISTINCT AUTHOR_ID) FROM BOOK
create.select(
count(BOOK.AUTHOR_ID),
countDistinct(BOOK.AUTHOR_ID),
groupConcat(BOOK.AUTHOR_ID),
groupConcatDistinct(BOOK.AUTHOR_ID))
.from(BOOK).fetch();
Producing:
+-------+----------------+--------------+-----------------------+ | count | count_distinct | group_concat | group_concat_distinct | +-------+----------------+--------------+-----------------------+ | 4 | 2 | 1, 1, 2, 2 | 1, 2 | +-------+----------------+--------------+-----------------------+
If DISTINCT is available through the jOOQ API, it is always appended to the aggregate function name, such as count() and countDistinct(). sum() and sumDistinct(), etc.
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