Add support for with clause

[artvandaly]

Could not find support for WITH clause
such as:

/* this example would return TOP 10 of most huge tables */
WITH
    (
        SELECT sum(bytes)
        FROM system.parts
        WHERE active
    ) AS total_disk_usage
SELECT
    (sum(bytes) / total_disk_usage) * 100 AS table_disk_usage,
    table
FROM system.parts
GROUP BY table
ORDER BY table_disk_usage DESC
LIMIT 10;

[sjoerdmulder]

Thank you for bringing this up. Currently there is no WITH support indeed. We are open for pull requests, so if you have some spare time, help is appreciated. Message ID: ***@***.***>

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