Develop Reference

SQLite Statement in Android Studio 3.5.3

I'm a newbie with Android Studio so please be patient... This forum often leads me with suggestions and examples (as a reader), but today I decided to ask for help:
Since hours, I try to build an SQLite statement in Android Studio: There is a column COLUMN_LAST_ATTEMPT with date and time as String, e.g. 2020-01-09 17:23, see screenshot, and I want to get the newest date (without time) from the table, e.g. 2020-09-01. I tried various options but I can't get it to run.
What I need is an Android SQLite Statement for
SELECT MAX(SUBSTR(last_attempt,11,20)) FROM quiz_questions
(which runs on DBBrowser), where 'last attempt' is a column of table 'quiz_questions', screenshot of that column in table 'quiz_questions'
I tried the following rawQueries, none of them works:
In QuizDBHelper-Class
//...
final QuizDbHelper dbHelper = QuizDbHelper.getInstance(this);
//...
public String newestQuiz(){
db = getReadableDatabase();
String result = null;
Cursor cursor = db.rawQuery("SELECT MAX(" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT + ") FROM "
+ QuizContract.QuestionsTable.TABLE_NAME, null);
//Cursor cursor = db.rawQuery("SELECT MAX(SUBSTR(" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT +
// ",11,20)) FROM " + QuizContract.QuestionsTable.TABLE_NAME, null);
//Cursor cursor = db.rawQuery("SELECT " + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT + " FROM " +
// QuizContract.QuestionsTable.TABLE_NAME, null);
if(cursor.moveToFirst()){
do {
result = cursor.getString(c.getColumnIndex(QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT));
} while (cursor.moveToNext());
}
cursor.close();
return result;
}
In Statistics-Class
String LastUse = dbHelper.newestQuiz();
LastUsage.setText("Letzte Challenge: " + LastUse);
//LastUsage is a TextView in activity_Statistics.xml
//attached with LastUsage = findViewById(R.id.text_lastUsage);
Either the SQLite statements are totally wrong or I make (basic?) mistakes in statistics class. I need ...newbie help!
I need something like Select column from table where substring of date-Entry == newest

Your issue appear to be column names. That is a Cursor only contains the columns extracted, not all the columns from the table. Although you are basing your query on the column as per QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT that will not be the column name in the cursor.
Rather it will will MAX(SUBSTR(" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT +
// ",11,20))
The simplest way of managing this is to give the column in the Cursor a specific name using AS. As such perhaps use :-
Cursor cursor = db.rawQuery("SELECT MAX(" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT + ") AS " + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT + " FROM "
+ QuizContract.QuestionsTable.TABLE_NAME, null);
However, you may prefere to use a column name (AS ????) specififc to the situation e.g.
........ AS max_" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT + ........
You would then have to use :-
result = cursor.getString(c.getColumnIndex("max_" + QuizContract.QuestionsTable.COLUMN_LAST_ATTEMPT));
Alternately, as it's just a single value/column that is returned in the cursor you could use the column offset of 0, in which case the column name is irrelevant as long as it is valid. However, using offsets is not typically recommended due to the lack of validation of the column being accessed.
re the comment :-
I just need the date part
As the date is a recognised DateTime format (and also that such formats are directly sortable/orderable), use max(date(column_name)) or even max(column_name).

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).

Why Sqlite return only last row not all rows data?

I don't know what's wrong with my code I follow the rule but I get wrong result. I want to search db and find all rows data but I only get last row from sqlite. my code to search database is bellow:
public ArrayList<ArrayList<ContractSaveDataFromDB>> ActiveContractData(String phone, String numberId)
{
ArrayList<ContractSaveDataFromDB> UserData = new ArrayList<ContractSaveDataFromDB>();
ArrayList<ArrayList<ContractSaveDataFromDB>> SendUserData =
new ArrayList<ArrayList<ContractSaveDataFromDB>>();
SQLiteDatabase db = this.getReadableDatabase();
String whereClause = "phone = ? AND numberId = ?";
String[] whereArgs = new String[]{
phone,
numberId
};
String orderBy = "activeContract";
Cursor res2=db.query("usersAccount",null,whereClause,whereArgs,null,null,orderBy);
res2.moveToFirst();
do{
UserData.clear();
int index;
ContractSaveDataFromDB contractSaveDataFromDB=new ContractSaveDataFromDB();
index = res2.getColumnIndex("buyAmount");
String buyAmount = res2.getString(index);
contractSaveDataFromDB.setBuyAmount(buyAmount);
UserData.add(contractSaveDataFromDB);
SendUserData.add(UserData);
} while(res2.moveToNext());
res2.close();
db.close();
return SendUserData;
I don't know what's wrong. I appreciate if you help me to solve my problem.

you already added where clause so maybe it is filtering your results try to remove it by change this
Cursor res2=db.query("usersAccount",null,whereClause,whereArgs,null,null,orderBy);
to this
Cursor res2=db.query("usersAccount",null,null,null,null,null,orderBy);

I believe that your issues is that you are trying to use an ArrayList of ArrayList of ContractSaveDataFromDB objects.
I believe that an ArrayList of ContractSaveDataFromDB objects would suffice.
It would also help you if you learnt to do a bit of basic debugging, as an issue could be that you are not extracting multiple rows.
The following is an alternative method that :-
uses the ArrayList of ContractSaveDataFromDB objects,
introduces some debugging by the way of writing some potentially useful information to the log
and is more sound, as it will not crash if no rows are extracted
i.e. if you use moveToFirst and don't check the result (false means the move could not be accomplished) then you would get an error because you are trying to read row -1 (before the first row) as no rows exists in the cursor.
:-
public ArrayList<ContractSaveDataFromDB> ActiveContractData(String phone, String numberId) {
ArrayList<ContractSaveDataFromDB> SendUserData = new ArrayList<ContractSaveDataFromDB>();
SQLiteDatabase db = this.getReadableDatabase();
String whereClause = "phone = ? AND numberId = ?";
String[] whereArgs = new String[]{
phone,
numberId
};
String orderBy = "activeContract";
Cursor res2 = db.query("usersAccount", null, whereClause, whereArgs, null, null, orderBy);
Log.d("RES2 COUNT", "Number of rows in Res2 Cursor is " + String.valueOf(res2.getCount()));
while (res2.moveToNext()) {
ContractSaveDataFromDB current_user_data = new ContractSaveDataFromDB();
current_user_data.setBuyAmount(res2.getString(res2.getColumnIndex("buyAmount")));
Log.d("NEWROW", "Adding data from row " + String.valueOf(res2.getPosition()));
SendUserData.add(current_user_data);
}
res2.close();
db.close();
Log.d("EXTRACTED", "The number of rows from which data was extracted was " + String.valueOf(SendUserData.size()));
return SendUserData;
}
If after running you check the log you should see :-
A line detailing how many rows were extracted from the table
A line for each row (if any were extracted) saying Adding data from row ? (where ? will be the row 0 being the first)
A line saying The number of rows from which data was extracted was ? (? will be the number of elements in the array to be returned)

Most recent added record into database

How should i get most recent added record from database, where COL_2 should == param that I pass into it.
I can get all records where COL_2 is equal to param with this code, but I need only recent one
public Cursor getRowsLast(String param) {
SQLiteDatabase db = helper.getWritableDatabase();
String[] COLS = new String[]{DatabaseHelper.COL_1,DatabaseHelper.COL_2, DatabaseHelper.COL_3,DatabaseHelper.COL_4};
String where = param;
Cursor c = db.query(true, DatabaseHelper.TABLE_NAME, COLS, DatabaseHelper.COL_2 + " = '" + where + "'", null, null, null, null, null);
if(c != null){
c.moveToFirst();
}
return c;
}

The most reliable way to get the most recent row in a table is to have a column defined in the table for the time of insert/update. Make sure this value is accurate at the time of insert/update, and create an index on it. You can then sort (descending) on this column to determine which one is the most recent - it will be the first row.

As the automatically generated ID values increase with every insert, the row with the highest ID will be the one that was inserted most recently. So add an 'order by _id desc' and the first row will be the most recently inserted one.
Note - this does not cover updates. If you need the row most recently inserted or updated, you'll have to use an additional timestamp column like Doug Stevenson suggested.

Android SQLite Repeated Elements

I have an issue with SQLite on android. Right now, I'm pulling a JSON object from a server, parsing it, and putting each sub-object in a Table with things such as the Name, Row_ID, unique ID, etc. using this code:
public void fillTable(Object[] detailedList){
for(int i=0;i<detailedList.length;++i){
Log.w("MyApp", "Creating Entry: " + Integer.toString(i));
String[] article = (String[]) detailedList[i];
createEntry(article[0], article[1], article[2], article[3], article[4], article[5]);
}
}
createEntry does what it sounds like. It takes 6 strings, and uses cv.put to make an entry. No problems.
When I try to order them however, via:
public String[] getAllTitles(int m){
Log.w("MyApp", "getTitle1");
String[] columns = new String[]{KEY_ROWID, KEY_URLID, KEY_URL, KEY_TITLE, KEY_TIME, KEY_TAGS, KEY_STATE};
Log.w("MyApp", "getTitle2");
Cursor c = ourDatabase.query(DATABASE_TABLENAME, columns, null, null, null, null, KEY_TIME);
Log.w("MyApp", "getTitle3");
String title[] = new String[m];
Log.w("MyApp", "getTitle4");
int i = 0;
int rowTitle = c.getColumnIndex(KEY_TITLE);
Log.w("MyApp", "getTitle5");
for(c.moveToFirst();i<m;c.moveToNext()){
title[i++] = c.getString(rowTitle);
Log.w("MyApp", "getTitle " + Integer.toString(i));
}
return title;
}
Each entry actually has many duplicates. I'm assuming as many duplicates as times I have synced. Is there any way to manually call the onUpgrade method, which drops the table and creates a new one, or a better way to clear out duplicates?
Secondary question, is there any way to order by reverse? I'm ordering by time now, and the oldest added entries are first (smallest number). Is there a reverse to that?

If you don't want duplicates in one column then create that column with the UNIQUE keyword. Your database will then check that you don't insert duplicates and you can even specify what should happen in that case. I guess this would be good for you:
CREATE TABLE mytable (
_id INTEGER PRIMARY KEY AUTOINCREMENT,
theone TEXT UNIQUE ON CONFLICT REPLACE
)
If you insert something into that table that already exists it will delete the row that already has that item and inserts your new row then. That also means that the replaced row gets a new _id (because _id is set to automatically grow - you must not insert that id yourself or it will not work)
Your second question: you can specify the direction of the order of if you append ASC (ascending) or DESC (descending). You want DESC probably.
Cursor c = ourDatabase.query(DATABASE_TABLENAME, columns, null, null, null, null, KEY_TIME + " DESC");