1. 查詢資料庫中某乙個欄位的個數統計
1.1. 根據統計的字段的個數進行降序排列並取前十
2. 根據乙個建立的表的值對另乙個表的值進行查詢
3. left join合併兩個表
select state, count(*) from location
left join (
select location_id from project)
on location.id = location_id
where country =='us'
group by state
order by count(*) desc
4. 將查詢結果當做乙個表
select pledged/count as pld_count,count(*),state from
(select count(*) as count, projectid from "comments"
group by projectid), project #結果表+project表
where id == projectid
group by pld_count
order by count(*) desc
5. 計算兩個字段相除
select g1,t2*1.0/t1as ratio from
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