查询表中字段TransOrderID唯一且OrderBackType=10，Status=30的数据

两个系统共用一张表，系统A和系统B数据类型有两种：20:回寄中30:已签收，系统A插入:10,系统B插入:20, 查询表中字段TransOrderID唯一且OrderBackType=10，Status=30的数据数量

表：orderbackdetail

 

 sql语句：

SELECT 
COUNT(1) AS Scaned
FROM
(SELECT TransOrderID, COUNT(TransOrderID) FROM orderbackdetail GROUP BY TransOrderID HAVING COUNT(TransOrderID)=1)tt 
LEFT JOIN `orderbackdetail` t2 ON  t2.`TransOrderID`=tt.`TransOrderID` 
WHERE  t2.`OrderBackType`=10 AND t2.`Status`=30