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docs: LIMIT n BY modifier

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f1yegor 2017-03-01 01:52:25 +01:00 committed by alexey-milovidov
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@ -2024,21 +2024,23 @@ If you have an ORDER BY clause with some small LIMIT after a GROUP BY, then ORDE
<h5>LIMIT N BY modifier</h5>
LIMIT %%N%% BY %%COLUMN%% allows you to restrict top %%N%% rows per each group of %%COLUMN%%
LIMIT %%N%% BY %%COLUMNS%% allows you to restrict top %%N%% rows per each group of %%COLUMNS%%. %%LIMIT N BY COLUMNS%% is unrelated to %%LIMIT BY%% clause. Key for %%LIMIT N BY%% could contain arbitrary number of columns and expressions.
Example:
%%SELECT
domainWithoutWWW(URL) AS domain,
domainWithoutWWW(REFERRER_URL) AS referrer,
device_type,
count() cnt
FROM hits
GROUP BY domain, referrer
GROUP BY domain, referrer, device_type
ORDER BY cnt DESC
LIMIT 5 BY domain
LIMIT 5 BY domain, device_type
LIMIT 100
%%
will select top 5 referrers for each domain.
will select top 5 referrers for each domain - device type pair, total number of rows - 100.
<h4>HAVING clause</h4>