Develop Reference

Avoid duplicate entries in SQLite

I am writing a small application in android to store basic details about person using SQLite.
I insert data using this function
public void insertData(String user,String p_no,SQLiteDatabase db)
{
ContentValues cv = new ContentValues();
cv.put(NAME, user);
cv.put(PHONE, p_no);
db.insert("MYTABLE", null, cv);
}
The above function allows duplicate names to be stored.
So I wrote a function that will first check whether a name exits and then enter.
public void insertData(String user,String p_no,SQLiteDatabase db)
{
Cursor resultSet=db.rawQuery("select NAME from MYTABLE where NAME = '"+user+"'",null);
if(resultSet==null)
{
ContentValues cv = new ContentValues();
cv.put(NAME, user);
cv.put(PHONE, p_no);
db.insert("MYTABLE", null, cv);
}
else Toast.makeText(context,user+" already exists",Toast.LENGTH_SHORT).show();
}
But the problem is now toast comes up every time I insert meaning even if the row is unique it is not inserted.
Why resultSet is not null even when there is no such row?

It is because RawQuery never returns null cursor, and that's what your checking criteria is, so it is failing always, and trying to add new value in DB.
I am not able to find the documentation where I learned it, but I will update as soon as possible.
You can check if you have values in cursor using -
if(cursor.moveToFirst())

because it is possible to have an empty cursor. Change your check like
if(cursor.getCount() == 0)
this way, if the cursor is not null, you check if it contains something too.
Probably this is not the best way to handle duplicates, in my opinion. You should mark your column as unique, and use insertWithConflict, to decide what to do in case you have already an entry with that value

Check
if (resultset.getCount() == 0)
Also, create Name as unique key to avoid duplicates. Instead of checking it everytime.

Create Android SQL Database with a few pre populate data

I've gone through many examples here, but all seem complicated and most of them are for large data. I'm new to both Android and also SQL. What I want to do is just pre-populate my SQL database with some data.
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE restaurants (_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, address TEXT, type TEXT, notes TEXT, feed TEXT, lat REAL, lon REAL);");
ContentValues cv=new ContentValues();
cv.put("name", "Hi");
cv.put("address", "There");
cv.put("type", "delivery");
cv.put("notes", "");
cv.put("feed", "");
cv.put("lat", "");
cv.put("lon", "");
getWritableDatabase().insert("restaurants", "name", cv);
}
There is no error but unfortunately no data is inserted as well. This should be very simple, please help me?

Use db.insert("restaurants", "name", cv);

Your approach is fine, inside SQLiteOpenHelper#onCreate() is the right place to put initial data since that is where you create the database in the state you like it to be.
But inside onCreate you use db.insert("restaurants", "name", cv) directly. You are not finished to create the writable database you try to get via getWritableDatabase() at that point. Not sure if that is the problem but it could be.

column is no created getting exception android

Well this is my DatabaseHelper class
public class DatabaseHelper extends SQLiteOpenHelper {
static final String dbName="demoDB";
public DatabaseHelper(Context context) {
super(context, dbName, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
String sql = "CREATE TABLE IF NOT EXISTS players (" +
"id INTEGER PRIMARY KEY AUTOINCREMENT, " +
"playerName TEXT)";
db.execSQL(sql);
ContentValues values = new ContentValues();
values.put("playerName", "John");
db.insert("players", "playerName", values);
values.put("playerName", "George");
db.insert("players", "playerName", values);
values.put("firstName", "Marie");
db.insert("players", "playerName", values);
System.out.println("Hello");
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS players");
onCreate(db);
}
}
And in my main activity this is what I do to get its data.
if (cursor!= null) {
if (cursor.moveToFirst()) {
do {
System.out.println(cursor.getString(cursor.getColumnIndexOrThrow("playerName")));
} while (cursor.moveToNext());
}
}
Why the column is not created?
and I am getting this exception.
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mkyong.android/com.mkyong.android.Stats}: java.lang.IllegalArgumentException: column 'playerName' does not exist

Are you selecting anything before you interact with the cursor? Your cursor should be the result from a "Select..." SQL call, but I don't see one in your DatabaseHelper or anything in your MainActivity to indicate you are doing any sort of selection.
Also, when you are inserting values into your table , I believe the second parameter should be null [db.insert("players", null, values)]. It's intended for the nullColumnHack, which you use if you aren't entering any data into row.
nullColumnHack optional; may be null. SQL doesn't allow inserting a completely empty row without naming at least one column name. If your provided values is empty, no column names are known and an empty row can't be inserted. If not set to null, the nullColumnHack parameter provides the name of nullable column name to explicitly insert a NULL into in the case where your values is empty.
Edit
Well, so far you've created a table and inserted some records. The next step would be to create basic CRUD operations (Create, Retrieve, Update, Delete), but for your case, you need to start with Retrieve.
Retrieve basically means you are reading/retrieving data from your database, so you can use it in your application. When you read the data from a DB, it gets stored in a Cursor. So, you need to:
Create a method in your database helper to read data from your database
From your main activity, call the method you created in step #1. Result is stored in a cursor.
In your main method, extract the data from the Cursor so you can use it. (Looks like you've already attempted this in your main activity).
Here is a link to a great tutorial on setting up a databse and how to create CRUD operations for your database. For now, scroll down and read up on the Retrieve operation.
http://www.androidhive.info/2011/11/android-sqlite-database-tutorial/
I would read the entire tutorial if I were you. There are lots of other helpful tips and suggestions that will be well worth the investment now. For example, creating constants in your DatabaseHelper class for the table name, database name, column name is a really good idea because sooner or later you're going to make a typo if you keep typing in all the column and table names manually. If you use variables, you'll get a compile error rather than an exception at runtime.

how to delete rows in a table on database using android sqlite3

i'm unable to delete row in a table using sqlite 3.In my code i would like to compare two
values an then delete the data in a table but it is not possible please help me.
while(authCur.moveToNext())
{
db.delete("auth_tab",authCur.getString(0)+"=?" , new String[] { user });
db.delete("auth_tab", null, null);
}

Deleting data
Once data is no longer needed it can be removed from the database with the delete() method. The delete() method expects 3 parameters, the database name, a WHERE clause, and an argument array for the WHERE clause. To delete all records from a table pass null for the WHERE clause and WHERE clause argument array.
db.delete("auth_tab", "authCur.getString(0)=?", new String[] {user);
Simply call the delete() method to remove records from the SQLite database. The delete method expects, the table name, and optionally a where clause and where clause argument replacement arrays as parameters. The where clause and argument replacement array work just as with update where ? is replaced by the values in the array.
or
public void deleteContact(long id) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(auth_tab, KEY_USER + " = ?",
new String[] { user) });
db.close();
}
WATCH more, and you tube video, how to delete.

Populate a list from a database in Android

I’m trying to query a single table database that I’ve created in my code. To the best of my knowledge the database is being created correctly. The query is supposed to be used to populate a ListView but when I try to use the resulting cursor from my query to create SimpleCursorAdapter, it crashes with: java.lang.IllegalArgumentException: column '_id' does not exist. I am assuming this can be traced to the cursor, and also the cursor seems to be empty.
The database is created in the following way within the onCreate() of my implementation of a SQLiteOpenHelper:
db.execSQL("CREATE TABLE " + TABLE_NAME + " (_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, name TEXT NOT NULL, title TEXT NOT NULL, path TEXT NOT NULL);");
And then the actual query is set up and executed in my DataHelper Class which is used to interact with the database:
public Cursor selectEntryStartsWith(String partialName , String title)
{
String where = "name LIKE '" + partialName + "%' AND title LIKE '" + title + "'";
if (title== null || title.equals("")){
where = "name LIKE '" + partialName + "%'";
}
Cursor cur = mDatabase.query(TABLE_NAME, new String[] {"_id", "name", "title"}, where, null, null, null, "name");
return cur;
}
The code that uses the cursor is as follows:
Cursor cursor = mDataHelper.selectEntryStartsWith("ex", null); //get all entries that start with "ex"
String [] from = new String [] { "name", "title" };
int [] to = new int [] { R.id.name, R.id.title };
SimpleCursorAdapter adapter = new SimpleCursorAdapter(mContext, R.layout.listview_entry, cursor, from, to);
songList.setAdapter(adapter);
I'm using tabs to this last piece of code is from within the onActivityCreated() of a Fragment; I not that it might be better to extend a ListFragment, but I don't think this is the problem here in particularity.
Sorry in advance if I have missed an information that you may require, I've been banging my head on this problem for some time now.

Do you know the data is actually in the database? Run 'adb shell', cd to your data directory '/data/data/[app package name]/databases'. Then run sqlite3 [db file name]. Run some direct sql queries and make sure data exists.
If there is data there, rather than going right to the SimpleCursorAdapter, run some text queries in code, and see if you can access the results.
Once all of that works out, add the ListView stuff as a last step.
Some things to mention. If the user is typing in query values, you need to escape those statement values. Either use selectionArgs in the query statement:
http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html#query(java.lang.String, java.lang.String[], java.lang.String, java.lang.String[], java.lang.String, java.lang.String, java.lang.String)
or use my stripped-down apache commons-lang, and the StringEscapeUtils class.
http://www.touchlab.co/blog/android-mini-commons/
Another thing to consider, although if you're not having trouble, its probably not an issue. 'name' and 'title' might be tricky keywords in sql statements.

The problem was indeed the database was not set up properly, I tried another method of inserting the data i.e. using ContentValues and inserting directly into the database, as opposed to using the precompiled insert statement I was using before.
The insert method now looks like this:
public long insert(String name, String title)
{
ContentValues cv = new ContentValues();
cv.put("name", name);
cv.put("title", title);
return mDatabase.insert(TABLE_NAME, null, cv);
/* The old code was using this precompiled statement
mInsertStatement.bindString(1, name);
mInsertStatement.bindString(2, title);
return mInsertStatement.executeInsert();
*/
}