哪些查询使用了物化视图？

问题：如何显示过去 60 分钟内涉及物化视图的所有查询？

回答

此查询将显示所有针对物化视图的查询，考虑到

• 我们可以利用 system.tables 表中的 create_table_query 字段来识别哪些表是 MV 的显式 (TO) 接收者；
• 我们可以使用 uuid 和名称约定 .inner_id.<uuid> 追溯哪些表是 MV 的隐式接收者；

我们还可以通过更改初始查询 CTE 中的值（默认情况下为 60 分钟）来配置我们希望回溯的时间长度

WITH(60) -- default 60m
AS timeRange,
(
    --prepare names of possible implicit MV hidden target tables for *any* table with NON NULL uuid
    SELECT groupArray(
            concat('default.`.inner_id.', toString(uuid), '`')
        )
    FROM clusterAllReplicas(default, system.tables)
    WHERE notEmpty(uuid)
) AS MV_implicit_possible_hidden_target_tables_names_array,
(
    --captures MV name and target tables (if TO is specified)
    --TODO it seems that extract will return just the first capturing group :( replace with regexpExtract once available
    SELECT arrayFilter(
            x->x != '',
            --remove empty captures
            groupArray(
                extract(
                    create_table_query,
                    '^CREATE MATERIALIZED VIEW\s(\w+\.\w+)\s(?:TO\s(\S+))?'
                )
            )
        )
    FROM clusterAllReplicas(default, system.tables)
    WHERE engine = 'MaterializedView'
) AS MV_explicit_target_tables_names_array
SELECT event_time,
    query,
    tables as "MVs tables"
FROM clusterAllReplicas(default, system.query_log)
WHERE (
        -- only SELECT within 60m
        event_time > now() - toIntervalMinute(timeRange)
        AND startsWith(query, 'SELECT')
    ) -- check either that query involves implicit MV target table names
    AND (
        hasAny(
            tables,
            MV_implicit_possible_hidden_target_tables_names_array
        )
        OR -- check that query involves explicit MV target table
        hasAny(tables, MV_explicit_target_tables_names_array)
    )
ORDER BY event_time DESC;

预期输出

| event_time          | query                                                                                          | MVs tables                                                            |
| ------------------- | ---------------------------------------------------------------------------------------------- | --------------------------------------------------------------------- |
| 2023-02-23 08:14:14 | SELECT     rand(),* FROM     default.sum_of_volumes,     default.big_changes,     system.users | ["default.big_changes_mv","default.sum_of_volumes_mv","system.users"] |
| 2023-02-23 08:04:47 | SELECT     price,* FROM     default.sum_of_volumes,     default.big_changes                    | ["default.big_changes_mv","default.sum_of_volumes_mv"]                |

在此示例中，上面的结果 default.big_changes_mv 和 default.sum_of_volumes_mv 都是物化视图。