В итоге вот так заработало:
SELECT
s1.page,
COUNT(s1.clientId ) AS step1,
COUNT(s2.clientId ) AS step2
FROM (
SELECT
page.pagePath AS page,
clientId
FROM
[limetest.limetableempty]
WHERE
page.pagePath CONTAINS 'url'
AND page.pagePath != 'utm_'
GROUP BY 1, 2
) s1
LEFT JOIN (
SELECT
clientId
FROM
[limetest.limetableempty]
WHERE
page.pagePath CONTAINS 'url'
AND page.pagePath != 'utm_'
GROUP BY 1
) s2
ON s1.clientId = s2.clientId
GROUP BY s1.page
SELECT
s1.page,
COUNT(s1.clientId ) AS step1,
COUNT(s2.clientId ) AS step2
FROM (
SELECT
page.pagePath AS page,
clientId
FROM
[limetest.limetableempty]
WHERE
page.pagePath CONTAINS 'url'
AND page.pagePath != 'utm_'
GROUP BY 1, 2
) s1
LEFT JOIN (
SELECT
clientId
FROM
[limetest.limetableempty]
WHERE
page.pagePath CONTAINS 'url'
AND page.pagePath != 'utm_'
GROUP BY 1
) s2
ON s1.clientId = s2.clientId
GROUP BY s1.page