SQL问题：合并2个查询结果为一个

Question

大佬们好，新手请教：
想把第二个查询的值加入到第一个查询里（相同日期的），没有的是0

第一个查询：

SELECT
date(visitdate) as days,
count(*) as total  
FROM visitor 
GROUP BY date(visitdate)  
ORDER BY days ASC

第二个查询：

SELECT date(askdate),count(*) as total2
FROM asknewuser
group by date(askdate)
order by date(askdate) asc

想要的结果：

Answer 1

SELECT t1.days,t1.total,IFNULL(t2.total2,0)
FROM
(
    SELECT
    DATE(visitdate) AS days,
    COUNT(*) AS total  
    FROM visitor 
    GROUP BY DATE(visitdate)    
)t1
LEFT JOIN 
(
    SELECT DATE(askdate) AS days,COUNT(*) AS total2
    FROM asknewuser
    GROUP BY DATE(askdate)
    ORDER BY DATE(askdate) ASC
)t2
ON t1.days=t2.days
ORDER BY t1.days ASC

上面的IFNULL函数是mysql的，如果是oracle，换成NVL