Develop Reference

Sqlite how to improve performance?

I have to make more than 300 selects from my database.
Each of those queries has to be called inside of a for each loop, here's an example:
for(int id : myids){
Cursor cursor = MyDatabaseHelper.runMyQuery(id);
while(cursor.moveToNext()){
//my stuff...
}
}
MyDatabaseHelper is an instance of a database helper class, the function is like this
public Cursor runMyQuery(int id){
SQLiteDatabase db = this.getWritableDatabase();
Cursor ret = db.rawQuery("select Name, Surname, Age from PTable where Id = " + id, null);
return ret;
}
I've been told that the constant "open and close" of the db because of multiple queries it the cause of my performance issues and I should, instead, make a single query (using union etc).
Changing my code to a single query would mean changing the entire database, and I was hoping not to do that.
Is there anything I can do to improve the performance and keep the multiple selects at the same time?
Thanks

I think what you are looking for is the in clause.
Convert your myids into a string. Something like
String inClause = "(1,2,3)"
and you can use it as
"select Name, Surname, Age from PTable where Id in " + inClause
You can read more of the in operator here

You can return a single Cursor containing all the rows.
First change your runMyQuery() method to this:
public Cursor runAll(String list){
SQLiteDatabase db = this.getWritableDatabase();
String sql = "select Name, Surname, Age from PTable where " + list + " like '%,' || id || ',%'"
Cursor ret = db.rawQuery(sql, null);
return ret;
}
So you pass to the method runAll() a String which is the the comma separated list of all the ids that you have in myids and with th eoperator LIKE you compare it to each id of the table.
You create this list and get the results in a Cursor object like this:
StringBuilder sb = new StringBuilder(",");
for(int id : myids){
sb.append(String.valueOf(id)).append(",");
}
String list = sb.length() > 1 ? sb.toString() : "";
if (list.length() > 0) {
Cursor c = runAll(list);
while(c.moveToNext()){
//your stuff...
}
}

Sql Query to retrieve a particular data from particular column and row in android?

I want to fetch phone number linked to particular email in the database. I am not able to find the query for it or how
public String getContactNumber(String email){
SQLiteDatabase db = this.getReadableDatabase();
String query = "SELECT " + COLUMN_USER_MOBILE_NUMBER + " FROM " + TABLE_USER + " WHERE " + email + " = " + COLUMN_USER_EMAIL;
Cursor cursor = db.rawQuery(query,null);
//What to put here to extract the data.
String contact = cursor.getString(get);
cursor.close();
return contact;
}
to extract the data. Completely a beginner

Try this ..
public List<String> getMyItemsD(String emailData) {
List<String> stringList = new ArrayList<>();
SQLiteDatabase db = this.getReadableDatabase();
String selectQuery = "SELECT COLUMN_USER_MOBILE_NUMBER FROM " + USER_TABLE_NAME + " WHERE email= " + emailData;
Cursor c = db.rawQuery(selectQuery, null);
if (c != null) {
c.moveToFirst();
while (c.isAfterLast() == false) {
String name = (c.getString(c.getColumnIndex("Item_Name")));
stringList.add(name);
c.moveToNext();
}
}
return stringList;
}

public String getContactNumber(String email){
String contact = "";
SQLiteDatabase db = this.getReadableDatabase();
String query = "SELECT " + COLUMN_USER_MOBILE_NUMBER + " FROM " + TABLE_USER + " WHERE " + email + " = " + COLUMN_USER_EMAIL;
Cursor cursor = db.rawQuery(query,null);
if(cursor.getCount()>0) {
cursor.moveToNext();
contact = cursor.getString(cursor.getColumnIndex(COLUMN_USER_MOBILE_NUMBER));
}
//What to put here to extract the data.
cursor.close();
return contact;
}
From this method you get phone number value of that email which you pass any other method easily.

I'd suggest the following :-
public String getContactNumber(String email){
String contact = "NO CONTACT FOUND"; //<<<<<<<<<< Default in case no row is found.
SQLiteDatabase db = this.getWritableDatabase(); //<<<<<<<<<< Generally getReadable gets a writable database
String[] columns_to_get = new String[]{COLUMN_USER_MOBILE_NUMBER};
String whereclause = COLUMN_USER_EMAIL + "=?";
String[] whereargs = new String[]{email};
Cursor cursor = db.query(TABLE_USER,columns_to_get,whereclause,whereargs,null,null,null);
//What to put here to extract the data.
if (cursor.moveToFirst()) {
contact = csr.getString(csr.getColumnIndex(COLUMN_USER_MOBILE_NUMBER));
}
cursor.close();
return contact;
}
The above does assumes that there will only be 1 row per email (which is most likely).
Explanations
A default value is set so that you can easily tell if an invalid/non-existent email is passed (you'd check the return value if need be (might be easier to simply have "" and check the length as a check)).
getReadableDatabase has been replaced with getWritableDatabase as unless there are issues with the database a writable database will be returned, as per :-
Create and/or open a database. This will be the same object returned
by getWritableDatabase() unless some problem, such as a full disk,
requires the database to be opened read-only. In that case, a
read-only database object will be returned. If the problem is fixed, a
future call to getWritableDatabase() may succeed, in which case the
read-only database object will be closed and the read/write object
will be returned in the future.
getReadableDatabase
Note no real problem either way;
The recommended query method has been used instead of the rawQuery method. This has distinct advantages, it builds the underlying SQL and also offers protection against SQL injection (just in case the email passed is input by a user).
this version of the method takes 7 parameters :-
The table name as a string
The columns to be extracted as an array of Strings (aka String array). null can be all columns.
The where clause less the WHERE keyword with ?'s to represent arguments (see next). null if no WHERE clause.
The arguments to be applied (replace ?'s 1 for 1) as a String array. null if none or no WHERE clause.
The GROUP BY clause, less the GROUP BY keywords. null if no GROUP BY clause.
The HAVING clause, less the HAVING keyword. null if no HAVING clause.
The ORDER BY clause, less the ORDER BY keywords. null if no ORDER BY clause.
SQLiteDatabase - query
- Note there are 4 query methods (see link for the subtle difference, I believe this is the most commonly used)
The data extraction is the new code. When a Cursor is returned it is at a position BEFORE THE FIRST ROW, so you need to move to a valid row. So the moveToFirst* method is suitable (note that if a move cannot be made by a move method that it will return false, hence how you can say if (cursor.moveToFirst())). The data is then extracted from the appropriate column use the **getString method, which takes an int as an argumnet for the column offset (0 in this case). However, using hard coded values can lead to issues so the getColumnIndex method is used to get the offset according to the column name (-1 is returned if the named column is not in the Cursor).

SQLite extracting day from date issue

I have a DATE field in my database with format 'YYYY-MM-DD'. Now I want to extract only 'day' from that day i.e. 'DD'. My table name is 'date' and the column name where date is stored is 'lastDonated'. How do i do it... please look these codes for more details.
public String day() {
String b = "";
SQLiteDatabase db = getWritableDatabase();
String query = "???(what to place in here?)";
Cursor c = db.rawQuery(query, null);
c.moveToFirst();
b = c.getString(c.getColumnIndex("lastDonated"));
c.moveToNext();
return b;
}
I only have one row in the database

Use this query
SELECT strftime('%d', YourDateColumn) AS SomeAlias FROM YourTable
And get the value like this
b = c.getString(c.getColumnIndex("SomeAlias"));
Reference: https://www.sqlite.org/lang_datefunc.html

How to select the remaining rows after selected some in Android SQLite?

I have a task in which i have to display the rows selected using a query in one tab and the remaining rows in another tab. I have displayed the selected rows using SimpleCursorAdapter. When i tried to display the remaining rows in next tab it throws error. I have tried NOT IN but it also doesn't work. I have tried NOT EXISTS also it shows all rows. Anyone who can answer please help. I have posted my code here. Thanks in advance.
This is the activity of first tab which displays selected rows
public class OnlineDevices extends Activity {
ListView listOnline;
DatabaseHelper databaseHelper;
String count;
int conut;
TextView tvOnlineCount;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_online_devices);
listOnline=(ListView)findViewById(R.id.listView3);
tvOnlineCount = (TextView) findViewById(R.id.textView59);
databaseHelper=new DatabaseHelper(this);
SQLiteDatabase db=databaseHelper.getReadableDatabase();
String date= DateFormat.getDateInstance().format(new Date());
String statusQuery="select rowid _id, deviceContact from statusTable where sentTime='"+date+"'";
Cursor cursor1=db.rawQuery(statusQuery,null);
if (cursor1.getCount()>0){
while (cursor1.moveToNext()){
String deviceNo=cursor1.getString(cursor1.getColumnIndex("deviceContact"));
String device=deviceNo.substring(2, 12);
String query="select rowid _id, userName, uSerialNo from bikeTable where uContactNo='"+device+"' AND userName IS NOT NULL";
Cursor cursor2=db.rawQuery(query, null);
SimpleCursorAdapter adapter=new SimpleCursorAdapter(this,R.layout.status_item,cursor2,new String[]{"userName","uSerialNo"},new int[]{R.id.textView51,R.id.textView52});
listOnline.setAdapter(adapter);
}
}
try {
conut = listOnline.getAdapter().getCount();
count = String.valueOf(conut);
tvOnlineCount.setText(count);
}catch (Exception e){
e.printStackTrace();
int i=0;
Toast.makeText(OnlineDevices.this,"No device is active",Toast.LENGTH_SHORT).show();
tvOnlineCount.setText(String.valueOf(i));
}
}
}
Activity for second tab which display the remaining rows are
public class OfflineDevices extends Activity {
ListView listOffline;
DatabaseHelper databaseHelper;
String deviceContact;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_offline_devices);
listOffline=(ListView)findViewById(R.id.listView4);
databaseHelper=new DatabaseHelper(this);
SQLiteDatabase db=databaseHelper.getReadableDatabase();
String date= DateFormat.getDateInstance().format(new Date());
String query="select rowid _id, deviceContact from statusTable where sentTime='"+date+"'";
Cursor cursor1=db.rawQuery(query,null);
if (cursor1.getCount()>0){
while (cursor1.moveToNext()) {
deviceContact = cursor1.getString(cursor1.getColumnIndex("deviceContact"));
}
String device=deviceContact.substring(2, 12);
String query2="select rowid _id, userName, uSerialNo from bikeTable where userName IS NOT NULL AND uContactNo='"+device+"'";
Cursor cursor3=db.rawQuery(query2,null);
String query1="select rowid _id,*from bikeTable where userName IS NOT NULL NOT IN('"+query2+"')";
Cursor cursor2=db.rawQuery(query1,null);
SimpleCursorAdapter adapter=new SimpleCursorAdapter(this,R.layout.status_item,cursor2,new String[]{"userName","uSerialNo"},new int[]{R.id.textView51,R.id.textView52});
listOffline.setAdapter(adapter);
}
}
}

You have syntax errors in your query. In theory the following should work:
String query2 = "SELECT userName FROM bikeTable WHERE userName IS NOT NULL "
+ "AND uContactNo = '" + device + "'";
String query1 = "SELECT * FROM bikeTable WHERE userName IS NOT NULL "
+ "AND userName NOT IN(" + query2 + ")";
Here are the differences:
Your original code has single quotes around query2 inside the parentheses. This makes SQLite treat it as a string literal instead of an inner query.
Since query2 is being used in a NOT IN expression, it needs to
have a single result column, and it seems like userName is the one
you are interested in.
I advise spending some time going through the SQLite language pages. I'm fairly certain you can actually get the results you want using a single query that has a JOIN instead of making one query, checking the result, then making another query.
As an aside, it's considered best practice in Android to load data from a database on a background thread. Typically this is done with the Loader framework. You should also be closing cursors when you are finished with them (not the ones you give to the adapters, but the ones you use just to check for an online device).

How to get the data for specify month and divide it by the number of days

I would like to check with you ,
I would like to do a summary for my application.
Such that it will give me an average for my price based on month.
This mean that I've a set of records, which I've already filter by month.
If month = Jan, I would like to get all the Jan data and divide by the number of days in the month.
Right now,
I'm only able to take out the months.
I would like to check,
If I would want to do " would like to get all the Jan data and divide by the number of days in the month. ", how can I do it?
Can anyone suggest to me?
Im new to android, and trying to learn things.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.summary);
monthDate = (EditText)findViewById(R.id.month);
avgPrice = (TextView)findViewById(R.id.showavfPriceTV);
exFuel = (TextView)findViewById(R.id.showexFuelTV);
avgFC = (TextView)findViewById(R.id.showavgFCTV);
doneButton = (Button)findViewById(R.id.doneBTN);
exitButton = (Button)findViewById(R.id.exitBTN);
// First we need to make contact with the database we have created using
// the DbHelper class
AndroidOpenDbHelper openHelperClass = new AndroidOpenDbHelper(this);
// Then we need to get a readable database
SQLiteDatabase sqliteDatabase = openHelperClass.getReadableDatabase();
// We need a a guy to read the database query. Cursor interface will do
// it for us
// (String table, String[] columns, String selection, String[]
// selectionArgs, String groupBy, String having, String orderBy)
Cursor cursor = sqliteDatabase.query(
AndroidOpenDbHelper.TABLE_NAME_LOG, null, null, null, null,
null, null);
// Above given query, read all the columns and fields of the table
startManagingCursor(cursor);
// Cursor object read all the fields. So we make sure to check it will
// not miss any by looping through a while loop
while (cursor.moveToNext()) {
// In one loop, cursor read one undergraduate all details
// Assume, we also need to see all the details of each and every
// undergraduate
// What we have to do is in each loop, read all the values, pass
// them to the POJO class
// and create a ArrayList of undergraduates
String id = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_ROWID));
final String date = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_DATE));
String price = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_PRICE));
String pump = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_FUEL));
String cost = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_COST));
String odm = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_ODM));
String preodm = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_PREODM));
String fcon = cursor.getString(cursor
.getColumnIndex(AndroidOpenDbHelper.KEY_CON));
// If you don't close the database, you will get an error
sqliteDatabase.close();
Log.i("FuelLog", "dataBundle " + date);
monthDate.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// showDialog(DATE_DIALOG_ID);
DialogFragment newFragment = new DatePickerFragment();
newFragment.show(getFragmentManager(), "datePicker");
}
});
doneButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (monthDate.getText().toString().equals(date.subSequence(3,9).toString()))
{
Log.d("MONTHDATE","date : "+ monthDate.getText().toString());
Log.d("BBUNDLEDATE","date : "+ (date.subSequence(3,9).toString()));
Intent intent=new Intent(getApplicationContext(),homeActivity.class);
startActivity(intent);
}
else
{
Intent intent=new Intent(getApplicationContext(),about.class);
startActivity(intent);
Log.d("ELSEMONTHDATE","date : "+ monthDate.getText().toString());
Log.d("ELSEBUNDLEDATE","date : "+ (date.subSequence(3,9).toString()));
}
}
});
}
}

Supposing you have the SUM of your monthly data for a single month,
Cursor cur = myDB.rawQuery
("SELECT SUM(Price) FROM Prices WHERE Month = 1", null);
if(cur.moveToFirst())
{
return cur.getInt(0);
}
Even better, you can have a single query to get the months and the summed prices per each month of the given year:
String sql = "SELECT Month, SUM(Price) FROM Prices WHERE Year = ? GROUP BY Month ORDER BY Month";
Divide your single monthly datum by:
Calendar cal = new GregorianCalendar(2014, Calendar.JANUARY, 1); // Specify an year and a month basing on your datum
int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
Just keep in mind this: (fromm the SQLite reference site)
sum(X) and
total(X)
The sum() and total() aggregate functions return sum of all non-NULL values in the group. If there are no non-NULL input rows then sum() returns NULL but total() returns 0.0. NULL is not normally a helpful result for the sum of no rows but the SQL standard requires it and most other SQL database engines implement sum() that way so SQLite does it in the same way in order to be compatible. The non-standard total() function is provided as a convenient way to work around this design problem in the SQL language.
The result of total() is always a floating point value. The result of sum() is an integer value if all non-NULL inputs are integers. If any input to sum() is neither an integer or a NULL then sum() returns a floating point value which might be an approximation to the true sum.
Sum() will throw an "integer overflow" exception if all inputs are integers or NULL and an integer overflow occurs at any point during the computation. Total() never throws an integer overflow.
ALSO NOTE
It's always a good idea to put dummy values (0.0) for months where no price is specified