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Merge pull request #46547 from den-crane/patch-62

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Doc. Better example of nested summing
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Alexey Milovidov 2023-02-18 17:20:57 +03:00 committed by GitHub
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docs/en/engines/table-engines/mergetree-family/summingmergetree.md
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@ -130,10 +130,57 @@ then this nested table is interpreted as a mapping of `key => (values...)`, and
Examples:
``` text
[(1, 100)] + [(2, 150)] -> [(1, 100), (2, 150)]
[(1, 100)] + [(1, 150)] -> [(1, 250)]
[(1, 100)] + [(1, 150), (2, 150)] -> [(1, 250), (2, 150)]
[(1, 100), (2, 150)] + [(1, -100)] -> [(2, 150)]
DROP TABLE IF EXISTS nested_sum;
CREATE TABLE nested_sum
(
date Date,
site UInt32,
hitsMap Nested(
browser String,
imps UInt32,
clicks UInt32
)
) ENGINE = SummingMergeTree
PRIMARY KEY (date, site);
INSERT INTO nested_sum VALUES ('2020-01-01', 12, ['Firefox', 'Opera'], [10, 5], [2, 1]);
INSERT INTO nested_sum VALUES ('2020-01-01', 12, ['Chrome', 'Firefox'], [20, 1], [1, 1]);
INSERT INTO nested_sum VALUES ('2020-01-01', 12, ['IE'], [22], [0]);
INSERT INTO nested_sum VALUES ('2020-01-01', 10, ['Chrome'], [4], [3]);
OPTIMIZE TABLE nested_sum FINAL; -- emulate merge
SELECT * FROM nested_sum;
┌───────date─┬─site─┬─hitsMap.browser───────────────────┬─hitsMap.imps─┬─hitsMap.clicks─┐
│ 2020-01-01 │ 10 │ ['Chrome'] │ [4] │ [3] │
│ 2020-01-01 │ 12 │ ['Chrome','Firefox','IE','Opera'] │ [20,11,22,5] │ [1,3,0,1] │
└────────────┴──────┴───────────────────────────────────┴──────────────┴────────────────┘
SELECT
site,
browser,
impressions,
clicks
FROM
(
SELECT
site,
sumMap(hitsMap.browser, hitsMap.imps, hitsMap.clicks) AS imps_map
FROM nested_sum
GROUP BY site
)
ARRAY JOIN
imps_map.1 AS browser,
imps_map.2 AS impressions,
imps_map.3 AS clicks;
┌─site─┬─browser─┬─impressions─┬─clicks─┐
│ 12 │ Chrome │ 20 │ 1 │
│ 12 │ Firefox │ 11 │ 3 │
│ 12 │ IE │ 22 │ 0 │
│ 12 │ Opera │ 5 │ 1 │
│ 10 │ Chrome │ 4 │ 3 │
└──────┴─────────┴─────────────┴────────┘
```
When requesting data, use the [sumMap(key, value)](../../../sql-reference/aggregate-functions/reference/summap.md) function for aggregation of `Map`.