Develop Reference

Android Database Query Cross-row Check

I am working on a project which requires me to do some query in android database. However, I am completely new to database and I am a little confused at how to deal with such scenarios. Here's a rough example to show my question.
For a table like this:
TableA:
--------------------------------------------------------
| _id | name | mimetype | data1 | data2 | data3 |
--------------------------------------------------------
| 1 | user1 | mime1 | val1 | val2 | x |
--------------------------------------------------------
| 2 | user1 | mime2 | val3 | val4 | y |
--------------------------------------------------------
| 3 | user1 | mime3 | val8 | val5 | a |
--------------------------------------------------------
| 4 | user2 | mime2 | val6 | val7 | q |
--------------------------------------------------------
| 5 | user2 | mime3 | val9 | val10 | a |
--------------------------------------------------------
| 6 | user3 | mime1 | val11 | val12 | b |
--------------------------------------------------------
Basically, I want to do a query to return data from columns of name, data1, data2 from TABLE A when it fits the following criteria:
mimetype = mime2
there's another row in the table that has the same name and its mimetype = mime3 and data3 = a
I am wondering how to do this in one query.
If anyone can give some direction on how to figure this out, it will be great! Thanks!

This can be done with the EXISTS operator and a correlated subquery:
SELECT ...
FROM TableA
WHERE mimetype = 'mime2'
AND EXISTS (SELECT 1
FROM TableA AS T2
WHERE T2.name = TableA.name
AND T2.mimetype = 'mime3'
AND T2.data3 = 'a');

Find difference of sum of column for different users

I want to find out difference of sum of debit and credit transactions of user and list them out.
Here is the query which i have tried out:
SELECT *, (val1 - val2)
FROM (SELECT *, sum(transactionAmount) AS val1
FROM tableTransaction
WHERE creditedToNum = My_Number
GROUP BY debtToNum) db
JOIN (SELECT *, sum(transactionAmount) AS val2
FROM tableTransaction
WHERE debtToNum = My_Number
GROUP BY creditedToNum) Cr
WHERE db.transactionStatus = 1
AND db.isActive = 1;
It's returning 0 rows but the actual output should be as below
Here is my table structure:
| Amount | Credit_to | Debit_to |
|--------|-----------|-----------|
| 2000 | My_Number | Number_1 |
| 5000 | My_Number | Number_2 |
| 3000 | Number_1 | My_Number |
| 4000 | Number_2 | My_number |
| 2000 | My_Number | Number_2 |
What actual result I want is:
| Name | Amount |
|----------|--------|
| Number_1 | 1000 |
| Number_2 | 3000 |

There is no join condition in your query.
Instead of joining, it might be a better idea to use a compound query to bring the data into a useful form:
SELECT Credit_to AS Name, Amount
FROM tableTransaction
WHERE Debit_to = #My_Number
UNION ALL
SELECT Debit_to, -Amount
FROM tableTransaction
WHERE Credit_to = #My_Number;
| Name | Amount |
|----------|--------|
| Number_1 | 3000 |
| Number_2 | 4000 |
| Number_1 | -2000 |
| Number_2 | -5000 |
| Number_2 | -2000 |
Then just group it:
SELECT Name, SUM(Amount) AS Total
FROM (SELECT Credit_to AS other, Amount
FROM tableTransaction
WHERE Debit_to = #My_Number
UNION ALL
SELECT Debit_to AS other, -Amount
FROM tableTransaction
WHERE Credit_to = #My_Number)
GROUP BY Name
ORDER BY Name;
| Name | Total |
|----------|-------|
| Number_1 | 1000 |
| Number_2 | -3000 |

Re-implement a preference screen in Android

In my app, I'm trying to have a list of custom servers, and I want to be able to add them and edit their respective settings individually.
The standard Android PreferenceFragment looks and works great for my purposes. Is there a way I can use it to edit selected items? Or, alternatively, can I re-create its look and behavior easily?
In a nutshell :
---------------- ----------------
| +| | |
| Item A | | Preference |
| Item B | --> Click on "A", "B" or "+" --> | Screen |
| ... | | |
| | | |
---------------- ----------------
Note that I also know how to use a screen hierarchy, and that doesn't fit the bill since I can't add or remove items dynamically, while the app is running.

From what I understand, you want to add preferences dynamically in your fragment.. Am I right??
Just look at this sample I found:
onCreate(){
this.setPreferenceScreen(createPreferenceHierarchy());
}
public PreferenceScreen createPreferenceHierarchy(){
PreferenceScreen root = getPreferenceManager().createPreferenceScreen(this);
// category 1 created programmatically
PreferenceCategory cat1 = new PreferenceCategory(this);
cat1.setTitle("title");
root.addPreference(cat1);
ListPreference list1 = new ListPreference(this);
list1.setTitle(getResources().getString(R.string.some_string_title));
list1.setSummary(getResources().getString(R.string.some_string_text));
list1.setDialogTitle(getResources().getString(R.string.some_string_pick_title));
list1.setKey("your_key");
CharSequence[] entries = calendars.getCalenders(); //or anything else that returns the right data
list1.setEntries(entries);
int length = entries.length;
CharSequence[] values = new CharSequence[length];
for (int i=0; i<length; i++){
CharSequence val = ""+i+1+"";
values[i] = val;
}
list1.setEntryValues(values);
cat1.addPreference(list1);
return root;
}//end method

How to iterate through a joined table with multiple results?

I have 3 tables, USER, ENTRY (for entered products, not necessary to create a PRODUCT table), and USER_COLLECTION, which is a table inbetween USER and ENTRY, because an entry can have multiple users.
Basically:
User = USERID | USER_NAME
Entry = ENTRYID | ENTRY_NAME | ENTRYPRICE | ENTRY_DATE
Collection = COLLECTIONID | ENTRYID | USERID
I have a table with users that persist throughout the project. They can create entries (which is usually some kind of product with a price) and they can link multiple users to a certain entry (which can be selected from a list, hence the users persist throughout the project).
So for instance, my tables look like this:
User
--------------------------
user_id | user_name
--------------------------
1 | 'FOO'
2 | 'BAR'
3 | 'FOOBAR'
ENTRY
-----------------------------------------------------------------------
entryid | entry_name | entry_price | entry_date
-----------------------------------------------------------------------
0 | 'Banana' | 2.50 | 12/12/2012
COLLECTION
---------------------------------------
collectionid | entryid | userid
----------------------------------------
0 | 1 | 1
1 | 1 | 2
2 | 1 | 3
I have a Banana, with a price of 2.50 and 3 users linked to it, Foo, Bar and Foobar.
Now, I want to use this in my app and get the data; except I don't know where to start. I tried selecting the entry data, using that id to loop through the collection data, but that would mean I have two cursors open and it wouldn't work. Tried creating a join but I couldn't really make a good one, mainly because:
JOIN
---------------------------------------
collectionid | entryname | username
----------------------------------------
0 | Banana | FOO
1 | Banana | BAR
2 | Banana | FOOBAR
I can't iterate through this, because I would create multiple of the same entry objects in my Android code...
Hope I'm being clear on this.
if (cursor2.moveToFirst()) {
do {
Item i = new Item(<GET STUFF FROM CURSOR>);
i.addUser(new Person(<GET STUFF FROM CURSOR>)));
Log.d("TAG", i.getUsersPaying().size() + "");
} while (cursor2.moveToNext());
}
If I use this, I create mulitple instances of Item i. They'll all be Banana, whilst I should only have 1 item Banana, with multiple users added to it.

First, you might want to consider returning the IDs from your tables in your join query. Things would be a little easier if you returned the entryid column.
Just make a Map<Integer, Item> to store items that you have seen already in your loop. As you examine each cursor, check the map to see if you already have an instance. If you don't, just make a new one and insert it.
Let's assume your query results are:
JOIN
----------------------------------------------------
collectionid | entryname | entryname | username
----------------------------------------------------
0 | 1 | Banana | FOO
1 | 1 | Banana | BAR
2 | 1 | Banana | FOOBAR
2 | 2 | Apple | FOOBAR
You can modify your code as follows:
Map<Integer, Item> items = new HashMap<Integer, Item>();
if (cursor2.moveToFirst()) {
do {
int itemId = cursor2.getInt(1);
Item i;
if (items.containsKey(itemId))
i = items.get(itemId);
else
{
i = new Item(<GET STUFF FROM CURSOR>);
items.put(itemId, i);
}
i.addUser(new Person(<GET STUFF FROM CURSOR>)));
Log.d("TAG", i.getUsersPaying().size() + "");
} while (cursor2.moveToNext());
}

You need to maintain a dictionnary of your entities which are already loaded in memory. For instance in a background fragment which would be retained.
Basically you would do:
Item i = cacheFragment.createOrGetEntry( cursor.getLong( ENTRY_ID_COLUMN_INDEX ) );
Person p = cacheFragment.createOrGetPerson( cursor.getLong( PERSON_ID_COLUMN_INDEX ) );
Of course, your query must also return the IDs of all the rows you need (entryId and personId). But a join query is the way to do it efficiently, so keep what you did about that and just add the two missing ID columns.
a createOrGetPerson method would look like:
public Person createOrGetPerson(long id) {
Entry<Long, Person> p = personDictionnary.get( id ); // can be a HashMap or even better, a SparseArray
if (p==null) {
p = new Person(id);
personDictionnary.put(p); // Remember it for next time
}
return p;
}
You should also have a look at data persistence frameworks or ORM frameworks which are made to deal with this kind of problem (e.g. Hibernate, even though I don't know if that is working with Android).

SQLite3 joining rows to form a single row

I am building an android application which queries a database for a bus number, and bus departure time.
The tables are thus -
Table 1: Route - _id, routenumber
Table 2: Routetimedetails - _id, routetime, routeid
My current query is this
select routenumber, route._id, routetime from route, routetimedata where route._id = 2 and routeid = route._id
and the result shows up like this
>
routenumber | route._id | routetime
-------------------------------------
BIAS10 | 2 | 0945
BIAS10 | 2 | 1810
BIAS10 | 2 | 1945
BIAS10 | 2 | 0710
is there a way in sqlite3 to show the result in a single column like this -
BIAS10 | 2 | 0710, 0945, 1810, 1945
Thanks
Mukul

I find that the Group_Concat() function does this easily
select routenumber, route._id, Group_concat(routetime) from route, routetimedata where route._id = 2 and routeid = route._id