JAVA 2018-05-31

mysql:

sql语句的if(when)写法

select c.terminal_num, sum(case c.statues_flag when 1 then c.run_time end) as sumrun1,sum(case c.statues_flag when 0 then c.run_time end) as sumrun2 from cardata_trip_statistics c GROUP BY c.terminal_num

根据 statues_flag字段 分别统计出run_time字段的值,  根据terminal_num分组(去重复)

mybatis:

多表关联的时候  sql语句用as名称    xml文件的model的属性 对应 as名称 就能映射字段了