在mysql中，同样在聚合函数中进行单位缩减，如果duration是varchar，计算会出错，duration是int就没问题
1 SELECT departure_city,SUM(duration) AS ‘SUM‘ 2 FROM `bus_route` 3 GROUP BY departure_city; 4 5 SELECT departure_city,SUM(duration/1000) AS ‘SUM‘ 6 FROM `bus_route` 7 GROUP BY departure_city;
SQL聚合函数中包含计算，列数据属性非数据格式则计算结果出错
原文：https://www.cnblogs.com/wawawawa-briefnote/p/12112142.html