SQLite查询返回空游标而不是0

Question

I have a query which should return total Income - total expense for the given date

db.rawQuery("select (totIncome-totExpense) from  " +
   "((select coalesce(sum(amount),0) as totIncome from transaction_table where type=0 and date like '"+ ke+"'), " +
   "(select COALESCE(sum(amount),0) as totExpense from transaction_table where type=1 and date like '"+ ke+"'))",null);

But when there are no records for type=0 , for a given date, the query returns an empty cursor instead of -totExpense .

Answer 1

You can do conditional aggregation with sum(case...) :

db.rawQuery(
  "select coalesce(sum(case type when 0 then amount else 0 end) - sum(case type when 1 then amount else 0 end), 0) as result from transaction_table where date like ?",
  new String[] {ke}
);

This way the sums are calculated with only one scan of the table.
The function coalesce() is needed only for the case that there are no rows in the table for that date.
I also took out from the query the date ke and passed it is a parameter, which is safer.
Maybe instead of like you can use = if ke is just a date and does not contain wildchars like % or _ .