MySQL计算百分比，我可以使用变量吗？

Question

我有一个查询，该查询返回 session 数量以及这些 session 中下的订单数量。很简单，但我想做的是显示下订单的 session 百分比。

SELECT COUNT(*) FROM table.session //Save this as variable 'Amount1'?
WHERE ses_Date BETWEEN ('2006/01/01') AND ('2011/01/01')
UNION ALL
SELECT COUNT(*) FROM table.session
WHERE Ses_ID
IN
(
SELECT Ses_ID FROM session //Save this as variable 'Amount2'?
JOIN table.order ON order.Session_ID = session.Ses_ID
WHERE ses_Date BETWEEN ('2006/01/01') AND ('2011/01/01')
GROUP by ses_ID
)

//Then do this, Display the percentage of the two
union all   
Select(SUM(amount2) /SUM(amount1) * 100)

在代码的评论中，我写了理论上我想做的事情，希望有所帮助。

Answer 1

你可以这样做:

SELECT COUNT(*) / (SELECT COUNT(*) 
                   FROM table.session
                   WHERE ses_Date BETWEEN ('2006/01/01') AND ('2011/01/01')) * 100

FROM table.session
WHERE Ses_ID
IN
(
SELECT Ses_ID FROM session //Save this as variable 'Amount2'?
JOIN table.order ON order.Session_ID = session.Ses_ID
WHERE ses_Date BETWEEN ('2006/01/01') AND ('2011/01/01')
GROUP by ses_ID
)