mysql-在限制范围内选择NULL值

我想在限制100之内选择NULL值.左联接应使输出限制为100,并且在其中我要计算所有NULL值.我的子查询似乎无法正常工作.有什么想法我做错了吗？提前致谢！

我用SUM()尝试了一些东西,但是那也行不通

SELECT SUM(echonest.id IS NULL) FROM (SELECT *
FROM tracks,echonest
left JOIN echonest ON tracks.id = echonest.id 
LIMIT 100)

SELECT *
FROM tracks AS t
LEFT JOIN echonest AS e ON t.id = e.id
LIMIT 100 IN 
(SELECT COUNT(e.id)
FROM e
WHERE e.id IS NULL)

预期的输出应计入LIMIT 100以内的所有NULL值.

最佳答案

我想这就是你想要的

SELECT COUNT(*) AS tot_nuls
FROM 
(
    SELECT E.id AS eid 
    FROM tracks T
    LEFT JOIN echonest E ON T.id = E.id 
    LIMIT 100
) T
WHERE eid IS NULL

但是,如注释中多次指定的那样,您应注意,没有ORDER BY子句的LIMIT子句将返回不确定的(又名随机的)结果.