Checking if the table has rows results in Null Pointer Exception in SQLiite Android

Question

I want to check if the table has rows and if it contains, then I want to delete it. Below is my code for checking if table has rows in it.

     boolean empty = true;
    Cursor cursor = db.rawQuery("SELECT count(*) FROM TABLE_NAME",null);
    cursor.moveToFirst();
    if (cursor.getInt(0) > 0)
    {
        empty = false;
    }
    else
    {
        empty= true;
    }
    return  empty;

I even tried checking with below code,

    boolean empty = true;
    Cursor cur = db.rawQuery("SELECT COUNT(*) FROM TABLE_NAME", null);
    if (cur != null && cur.moveToFirst()) {
        empty = (cur.getInt (0) == 0);
    }
    cur.close();

    return empty;

Both of the above code, throws NullPointerException in line

("SELECT COUNT(*) FROM TABLE_NAME", null);

Any help would be great !! Thanks

post the exception also...It may seems that your `db` object is `null`. — ELITE, May 07 '16 at 05:55
better to do `int count = cur.getCount();` is return the effected rows. — M D, May 07 '16 at 05:56
@MD `Cursor#getCount()` is kinda pointless on a `COUNT` query. — Mike M., May 07 '16 at 05:58
@MD "select count(*)" will always have one row (even if the table is empty), so in this case `getCount() == 1` — pskink, May 07 '16 at 06:03
But why its throwing null pointer exception in raw query line ? @pskink — Anusha, May 07 '16 at 06:14
Yea i didn't initialize db its not throwing exception now but its not deleting the data from the table. I want to delete records if there is data in database. I think the above code returns false @pskink — Anusha, May 07 '16 at 06:27
it returns false if `cursor.getInt(0) > 0` is it really what you want? — pskink, May 07 '16 at 06:36

score 1 · Answer 1 · edited May 07 '16 at 06:17

Android comes with a utility class called DatabaseUtils which has a method queryNumEntries that can take your database object and table name as parameter and return the total number of records on that database. Quite a clean way. You don’t need to be writing ‘Select Count(*) from mytable‘ kind of stuffs.

public long count() {
    return DatabaseUtils.queryNumEntries(db,'myTablename');
}

next to delete he rows if your database is not empty try deleteAll to delete all the rows in dB, or use delete_byID() by passing the ID as parameter to the row which you want to delete.

public int deleteAll(){
    return sqLiteDatabase.delete(MYDATABASE_TABLE, null, null);
}

public void delete_byID(int id){
    sqLiteDatabase.delete(MYDATABASE_TABLE, KEY_ID+"="+id, null);
}

This does not answer the question. – CL. May 07 '16 at 06:18 — CL., May 07 '16 at 06:18

Checking if the table has rows results in Null Pointer Exception in SQLiite Android

1 Answers1