Question

I’ve added 3 strings of data into a SQL database in android. A fourth string makes up the database, however it is a date:

SimpleDateFormat outputDate = new SimpleDateFormat(yyyy-MM-dd)

Date outputDate = new Date();

When the user enters information to the database, the adding method for the database creates the date, which is added to the database.

My question is, how can I use these imported dates to create a method whereby only the rows in the database that were added on in the last 31 days?

A SELECT method comes to mind through research, but I don’t know how to implement it?

Thanks

Answer 1

As long as you ask about Android I assume that the database you use is SQLite. SQLite does not have datatype for date. Thus you have couple of options: store the date in string (like you did) or store the timestamp of the date.

I seriously recommend you to use the second option as it is going to convert your dates in integers and it will be even easier to handle.

Thus when you want to select only events in the last 31 days you can do:

SQLiteDatabase database = helper.getWriteableDatabase();
final long millisIn31Days = 31 * 24 * 60 * 60 * 1000; 
String where = "<your-date-column> >= ?"
String [] whereArgs = { String.valueOf(new Date().getTime() - millisIn31Days) };
Cursor cursor =
    database.query("<TABLE_NAME>", null, where, whereArgs, null, null, null);

Note that here I write in angular brackets all the values you should actually fill in with the correct constants.

If you, however, want to stick to the string solution, you can still go with string comparison, as long as you specify the date format in correct manner (yours seems to be like that). In the string solution you will need to calculate the date of 31 days ago. You can use the Calendar‘s class auxiliary methods to achieve that.