mysql查询与group by不接收零值

Question

从我的查询中我只收到非零值。为什么呢？

SELECT
    CAST( `start`  AS DATE), COUNT(`msisdn`) 
FROM 
    `master`
WHERE
    `server_no`='105' 
AND CAST( `start`  AS DATE) BETWEEN '2015-08-20'  
AND '2015-08-31' GROUP BY CAST( `start`  AS DATE), `msisdn`   
AND `msisdn` LIKE '+9472%' OR `msisdn` LIKE '9472%';";  

第一行值应为零，但不是。为什么呢？