查詢時函數處理後的字段的別名無法作爲 where 的條件，可以作爲 having 的條件，這時用 having 篩選後再分組就會報錯，因爲 having 不能用在 group by 之前，所以我們可以先把 having 篩選後的記錄作爲一個整體，然後再去分組，代碼如下。
select count(one.keywrod) as num one.keyword (select A.a as keyword, B.b from A
left join B on A.a = B.b
where A.c = ""
having keyword = B.z) as one
group by one.keyword
