Android SQLite性能：單個查詢中的多個選擇與多個查詢中的單個選擇？

Question

性能方面，哪一個更好（單個表）：

1. 在單個查詢多選或
2. 單選擇多個查詢？

例子：

/*table schema*/ 
create table ACTIVITY_TABLE (
ID integer primary key autoincrement, 
INTERVAL_ID integer not null, 
ACTIVITY_TYPE text , 
WIFI_LIST text, 
COUNT integer not null); 



/*Multipe selects in single query*/ 
select * from 
    (select sum(COUNT)/60 as Physical from ACTIVITY_TABLE where INTERVAL_ID >=1 and INTERVAL_ID <=3 and (ACTIVITY_TYPE="Still" or ACTIVITY_TYPE = "Walking" or ACTIVITY_TYPE = "Running" )), 
    (select sum(COUNT)/60 as vehicular from ACTIVITY_TABLE where INTERVAL_ID >=1 and INTERVAL_ID <=3 and (ACTIVITY_TYPE="InVehicle")); 

Answer 1

對於你的榜樣，您可以修改通過以下方式，這將是更有效的查詢，我沒有測試查詢。

select 
sum(case when activitytype='walking' or activitytype='still' or activitytype='running' then COUNT else 0 end)/60 as physical, 

sum(case when activitytype='InVehicle' then COUNT else 0 end)/60 as vehicular 

from 

activity_table 

where interval_id>=1 and interval_id<=3