Develop Reference

Why cursorObject.moveToFirst() is required on updating my database table value

I had a problem with updating of a column's value at a particular row. I had written
Cursor c = mDb.rawQuery("UPDATE "+book+" SET footnotes='" + note + "' WHERE chapter="+chapter+" and verse="+verse+"", null);
c.close();
But on adding c.moveToFirst() it worked. Why is that?
Cursor c = mDb.rawQuery("UPDATE "+book+" SET footnotes='" + note + "' WHERE chapter="+chapter+" and verse="+verse+"", null);
c.moveToFirst();
c.close();
Why is c.moveToFirst() necessary here, any particular reason?
There is an explation for c.moveToFirst()
(What is The use of moveToFirst () in SQLite Cursors) which briefly suggests that using c.moveToFirst() does two things
allows you to test whether the query returned an empty set
moves the cursor to the first result
But how does the above two things help in updation?

Think of rawQuery() as a wrapper for the C library sqlite3_prepare_v2() that compiles the SQL but does not run it, while think of moveTo..() as a wrapper for sqlite3_step() that is required for actually executing the prepared statement.
Related: What is the correct way to do inserts/updates/deletes in Android SQLiteDatabase using a query string?

How to get 5 last record in the sqlite db in android?

Since the db does not have create date and some ordering field (but in my observation the last row is the latest record),
so how can i get the five last record in some condition e.g.
five record that their schoolid == 1?
Thanks
public Cursor select()
{
String orderBy = FIELD_pubKey+" DESC";
Cursor cursor = iReadDatabase.query(TABLE_NAME, null, null, null, null, null, orderBy);
cursor.moveToFirst();
return cursor;
}

There's no such thing as a last record or a first or a 42nd.
Which records appears last in the result of a query is dependent on the query plan, or an Explicit order by if you add one.
Select * From Table Where ...
The rows will be returned in whatever order the engine considers suitable at the time.
If you need them in specific order, then add an order by clause to the query, anything else is asking for it.
Something like
Select * From Table Order by SomeColumn desc limit 5
will do what you require.
Now what column you need to order by I've no idea, but you need one that will do the job, assuming automatic primary key, but note it is possible to mess with that.

Default order of records returned by cursor was not same for mobile & tablet

I wrote a select query to access set of records from database by setting null for the argument 'orderBy' in the query(). I found that order of records returned by query() method when I run the application in mobile is completely different when I run the same sample application in tablet.
My Query:
Cursor cursor = database.query(true, tableName, downloadQueueTableColumnNames, selection, null, null, null, null, null);
Here, in the query orderBy field is null.
I hope someone to explain the reason behind this...

If you aren't ordering the results, they can be returned in any order. The same device doesn't have to give the same order if you call it twice in a row. If you want it in the same order every time, you must use an order by.

Queue SUM of SQLite column - android

I have a listview populated from an SQLite database. I have several items that I successfully populate into the listview, however I'm having trouble with one last thing.
I'm trying to queue the sum total of the column KEY_CONTENT6 which is a string type, however it only contains numbers. I'd like to keep it as a string, so to add it up I'm using Double.valueOf(). The problem is this code force closes on queue and I cant figure out whats wrong:
public Cursor queueAll(){
String[] columns =
new String[]{KEY_ID, "sum("+ Double.valueOf(KEY_CONTENT6) +")",
KEY_CONTENT9, KEY_CONTENT10 };
Cursor cursor = sqLiteDatabase.query(MYDATABASE_TABLE, columns,
null , null, KEY_CONTENT10, null, KEY_CONTENT9+ " DESC");
return cursor;
}

simply use SUM, no need to use anything else..
String[] columns =
new String[]{KEY_ID, "sum(KEY_CONTENT6)",
KEY_CONTENT9, KEY_CONTENT10 };
It is valid for SQLite. Because, no matter what you set data type in SQLite, it stores values as string. So, type conversion is somewhat built-in in SQLite.

You can't use java in a SQL statement, either stick to strait sql or iterate over the cursor and use java to do your calculation.
You can find everything there is to know about sqlite here http://www.sqlite.org/docs.html

SQLite is basically typeless, so you might be able to use SUM on your column even though it is a string. However, if it's meant to be a numeric column, why not give it a number type??

Android SQLite and Bind Variables Problem

I'm trying to do a relatively simple bitwise query operation with SQLite on Android. When I use bind variables, I get no data returned when I believe should get some rows back. If I hardcode the bind variable's value directly into the SQL, it works just fine. I'm thinking I have some silly syntax issue somewhere, but I just can't see it.
So this code works just fine:
String selection = new String(FLAGS + " & 2 = 2");
cursor = db.query(TABLE_NAME, ALL_COLUMNS, selection,
null, null, null, null, null );
This code however (using bind variables), returns no rows:
String selection = new String(FLAGS + " & ? = ?");
String[] selectionArgs = new String[]{"2", "2"};
cursor = db.query(TABLE_NAME, ALL_COLUMNS, selection,
selectionArgs, null, null, null, null );
They both result into a syntactically identical query being built when I inspect the cursor's mQuery property through the debugger. The latter does have the mBindArgs property populated correctly as well. I'm at a loss as to how this could be failing. There are no exceptions thrown or anything, it just doesn't return any rows.
I can take the failing query, and manually swap the question marks for the two's and paste it into the ADB SQLite command line interface and it works just fine as well.

If I am right the second query produces following condition:
& '2' = '2'
instead of
& 2 = 2
Try replacing & with AND
Make sure you have no ? characters in FLAG constant.
Besides what is a point of this logical condition?

I was facing the same problem as yours. As radek-k said, the query compares string.
One solution that may be performed is to use the following:
String selection = new String(FLAGS + " & ? = (0|?)");