我如何 select 唯一键，数组中的值对到 Clickhouse 中的物化视图？

Question

table结构如下，

CREATE TABLE metrics

(
    `created_date` Date,
    `created_at` DateTime,
    `host` LowCardinality(String),
    `metrics_name` LowCardinality(String),
    `tags` Nested(key LowCardinality(String), value LowCardinality(String))
)
ENGINE = MergeTree(created_date, (created_at), 8192)

如何生成结构类似于

的物化视图

Host	Key	Values
host	Key: X	Values : ["uniq1", "uniq2"]

Answer 1

考虑使用这个 MV：

CREATE MATERIALIZED VIEW metrics_mv
ENGINE = MergeTree()
ORDER BY host AS
SELECT
    host,
    tags.key key,
    groupArray(tags.value) values /* or 'groupUniqArray(tags.value) AS values' to get unique values */
FROM metrics
ARRAY JOIN tags
GROUP BY
    host,
    tags.key

Answer 2

MergeTree(created_date, (created_at), 8192)

此语法在 3 年多以前就已过时。尽量不要使用它。它最终会被取消。

ENGINE = MergeTree partition by toYYYYMM(created_date) ORDER by (created_at)

CREATE TABLE metrics
(
    `created_date` Date,
    `created_at` DateTime,
    `host` LowCardinality(String),
    `metrics_name` LowCardinality(String),
    `tags` Nested(key LowCardinality(String), value LowCardinality(String))
)
ENGINE = MergeTree partition by toYYYYMM(created_date) ORDER by (created_at)


create materialized view metrics_mv (
     host LowCardinality(String),
     key LowCardinality(String),
     u_values SimpleAggregateFunction(groupUniqArrayArray, Array(String))
)     
Engine=AggregatingMergeTree order by (host, key) as
select host, 
       tags.key as key, 
       groupUniqArray(tags.value) as u_values
from metrics array join tags
group by host, key


insert into metrics values(today(), now(), 'h1', 'm1', ['k1','k2'], ['v1', 'v2']);
insert into metrics values(today(), now(), 'h1', 'm1', ['k1','k2'], ['v1', 'v2']);
insert into metrics values(today(), now(), 'h1', 'm1', ['k1','k3'], ['v11', 'v2']);
insert into metrics values(today(), now(), 'h2', 'm1', ['k1','k3'], ['v1', 'v22']);

optimize table  metrics_mv final;

select * from metrics_mv;

┌─host─┬─key─┬─u_values─────┐
│ h1   │ k1  │ ['v11','v1'] │
│ h1   │ k2  │ ['v2']       │
│ h1   │ k3  │ ['v2']       │
│ h2   │ k1  │ ['v1']       │
│ h2   │ k3  │ ['v22']      │
└──────┴─────┴──────────────┘

select host, key, groupUniqArrayArray(u_values) values
from metrics_mv
group by host, key

┌─host─┬─key─┬─values───────┐
│ h1   │ k2  │ ['v2']       │
│ h2   │ k3  │ ['v22']      │
│ h1   │ k3  │ ['v2']       │
│ h1   │ k1  │ ['v11','v1'] │
│ h2   │ k1  │ ['v1']       │
└──────┴─────┴──────────────┘

我如何 select 唯一键，数组中的值对到 Clickhouse 中的物化视图？

How do I select unique key, value pairs from an array into a materialized view in Clickhouse?

sql

materialized-views

clickhouse