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How can I change the order of my recyclerView items by changing values in the database?

In my app, the user should be able to change the order of the item. I am having the data from the table by SELECT statement order by Order field, and storing the result in the List. Then I am showing the List data in the Recycler View.
I would like to move "Item 5 " from recycler view position 4, and Order field value 12 to recycler view position 1.
My first question :
How do I move the Item 5 to recycler position 1 using Java/Kotlin?
My second question:
How do I move the Item 5 to recycler position 1 and change the Order field in DB accordingly? Means when I move the Item 5 to recycler position 1 the Item 5 Order field should change to 5,
Item 2 Order field should change to 7,
Item 3 Order field should change to 9 ,
Item 4 Order field should change to 12
The Recycler View items:

Answer one, rebuild/refresh the recyclerview with new data after changing the database.
Answer two
Roughly speaking you have to
ascertain the range of the affected rows (those whose order is between the from an to)
shift the values of the affected rows that are NOT the row being moved using the value from the next row in the direction of the move
change the value in the moved row
This is quite complex especially if all of the stages are to be combined. However, this is achievable with SQLite using Common Table Expressions (temporary tables that exist just for the duration of the query).
The following is a demonstration that solves the issue posed i.e. changing from:-
to
This is the demo (commented and formatted) that demonstrates the core query that would be implemented in Room (the comments indicate the core query):-
/* Just in case the environment has not been cleanup, clean it up*/
DROP TABLE If EXISTS example;
/* Create the table to be demonstrated */
CREATE TABLE IF NOT EXISTS example (
orderinrecyclerview INTEGER,
orderfieldvaluesfromtable INTEGER,
textfieldvaluesfromtable TEXT
);
/* Add the data for the demo */
INSERT INTO example VALUES
(0,2,'Item 1'),
(1,5,'Item 2'),
(2,7,'Item 3'),
(3,9,'Item 4'),
(4,12,'Item 5'),
(5,16,'Item 6')
;
/* Show the original data as RESULT 1 */
SELECT * FROM example ORDER BY orderfieldvaluesfromtable;
/*<<<<<<<<<< THIS IS THE CORE QUERY BEING DEMONSTRATED >>>>>>>>>>*/
WITH
/* CTE (Common Table Expression which is temp table that exists only for the duration of the query)
store the from and to values for the move to be made,
so values can be obtained whenever needed
*/
cte_args(fromvalue,tovalue) AS (
SELECT
12 /* will not be hard coded but passed/bound via arg*/,
5 /* will not be hard coded but passed/bound via arg */
) /* from to values*/,
/* Second CTE to get all the rows that will be affected, along with the new replacement value */
/* This is done in two stages
stage one gets all affected rows EXCEPT the actual row being moved.
stage two gets the actual row being changed
*/
cte_rowstochange(rowid,originalorder,neworder) AS (
SELECT
rowid, /* the rowid (always exists for tables unless WITHOUT ROWID table (ROOM does not support WITHOUT ROWID tables)) */
orderfieldvaluesfromtable,
(
SELECT orderfieldvaluesfromtable
FROM example
WHERE orderfieldvaluesfromtable > e.orderfieldvaluesfromtable /* e is the primary query example table as opposed to subquery example table */
ORDER BY orderfieldvaluesfromtable ASC /* want the next higher */
LIMIT 1 /* only want the 1 value */
) /* The value of the order in the next row (next higher order) */
FROM example AS e /* need to alias the table for WHERE clause above which accesses the same table */
WHERE orderfieldvaluesfromtable >= (SELECT tovalue FROM cte_args)
AND orderfieldvaluesfromtable < (SELECT fromvalue FROM cte_args)
UNION ALL SELECT
rowid,
orderfieldvaluesfromtable,
(
SELECT tovalue FROM cte_args
)
FROM example
WHERE orderfieldvaluesfromtable = (SELECT fromvalue FROM cte_args)
ORDER BY orderfieldvaluesfromtable ASC
)
UPDATE example
SET orderfieldvaluesfromtable = (
SELECT neworder
FROM cte_rowstochange
WHERE example.rowid = cte_rowstochange.rowid
)
WHERE rowid IN (
SELECT rowid FROM cte_rowstochange
)
;
/*<<<<<<<<<< END OF THE CORE QUERY >>>>>>>>>>*/
SELECT * FROM example ORDER BY orderfieldvaluesfromtable;
/* Cleanup testing environment */
DROP TABLE If EXISTS example;
To use the above in Room, then you just need the core query (adjusted to table args for the from an to values) e.g. :-
Query("WITH cte_args(:fromvalue,:tovalue) AS (SELECT 12,5),cte_rowstochange(rowid,originalorder,neworder) AS (SELECT rowid,orderfieldvaluesfromtable,(SELECT orderfieldvaluesfromtable FROM example WHERE orderfieldvaluesfromtable > e.orderfieldvaluesfromtable ORDER BY orderfieldvaluesfromtable ASC LIMIT 1) FROM example AS e WHERE orderfieldvaluesfromtable >= (SELECT tovalue FROM cte_args) AND orderfieldvaluesfromtable < (SELECT fromvalue FROM cte_args) UNION ALL SELECT rowid,orderfieldvaluesfromtable,(SELECT tovalue FROM cte_args) FROM example WHERE orderfieldvaluesfromtable = (SELECT fromvalue FROM cte_args) ORDER BY orderfieldvaluesfromtable ASC) UPDATE example SET orderfieldvaluesfromtable = (SELECT neworder FROM cte_rowstochange WHERE example.rowid = cte_rowstochange.rowid) WHERE rowid IN (SELECT rowid FROM cte_rowstochange);")
fun moveOrderDown(fromvalue: Int,tovalue: Int)
NOTE obviously the component names (tables and columns therein) would have to be changed to suit the actual tables and columns i.e.
the tablename example would have to be changed to reflect whatever that table is
column orderfieldvaluesfromtable would have to be changed.
Other component names can remain as is i.e.
rowid, e, tovalue, fromvalue, neworder, cte_args and cte_rowstochange
all except rowid could be changed consistently if required. rowid MUST be rowid it is the name of a hidden column that exists in all tables that are not WITHOUT ROWID tables or virtual tables (none of which Room supports directly (full text search aka FTS being an exception)).
Important
The above just solves moving an order to a lower order. The logic for the move to a higher order would be similar but reversed. You would likely want a moveOrderUp function. You could perhaps have a third function that determines which move function to invoke e.g.
fun moveOrder(fromvalue: Int, tovalue: Int) {
if (fromvalue == tovalue) return
if (fromvalue > tovalue) {
moveOrderDown(fromvalue,tovalue)
} else {
moveOrderUp(fromvalue,tovalue)
}
}
Further more the solution is in-principle and has not been exhaustively tested and may therefore have undetected issues.

How implement friends Relationship android

I'm trying to implement some code for get friends list.
First:
- I have my String id. E.G: 784717
- I have an string with 100 numbers. E.G: 7781,5913,551949194,4919491,...,444131 (One string separated by ,)
- I have 3000 records in my Database with different numbers. (With numbers I mean some kind of ID)
- Of my 100 numbers only 8 are registered in my database.
Question:
How can I know what numbers are registered in the database and insert in other table the relationship?
My table Relationship have this columns:
*number1 - (Here should be my ID)
*number2 - (1 of the 100 numbers that exists)
So in my table Relationship should be 8 new rows.
I tried with :
EXEC('SELECT * FROM Accounts WHERE ID IN(' +#in_mystring+')')
but i don't know how insert in the other table or if is efficiently

Assuming this is SQL Server, and with the help of a parser function
For example
Select * from [dbo].[udf-Str-Parse]('7781,5913,551949194,4919491,...,444131',',')
Returns
Key_PS Key_Value
1 7781
2 5913
3 551949194
4 4919491
5 ...
6 444131
From this sub-query, you can join the results to your Accounts Table
Perhaps something like this
Select A.*
From Accounts A
Join (Select * from [dbo].[udf-Str-Parse]('7781,5913,551949194,4919491,...,444131',',')) B
on A.Key_Value =A.ID
The UDF -- If 2016, There is a native parser.
CREATE FUNCTION [dbo].[udf-Str-Parse] (#String varchar(max),#delimeter varchar(10))
--Usage: Select * from [dbo].[udf-Str-Parse]('Dog,Cat,House,Car',',')
-- Select * from [dbo].[udf-Str-Parse]('John Cappelletti was here',' ')
-- Select * from [dbo].[udf-Str-Parse]('id26,id46|id658,id967','|')
Returns #ReturnTable Table (Key_PS int IDENTITY(1,1) NOT NULL , Key_Value varchar(max))
As
Begin
Declare #intPos int,#SubStr varchar(max)
Set #IntPos = CharIndex(#delimeter, #String)
Set #String = Replace(#String,#delimeter+#delimeter,#delimeter)
While #IntPos > 0
Begin
Set #SubStr = Substring(#String, 0, #IntPos)
Insert into #ReturnTable (Key_Value) values (#SubStr)
Set #String = Replace(#String, #SubStr + #delimeter, '')
Set #IntPos = CharIndex(#delimeter, #String)
End
Insert into #ReturnTable (Key_Value) values (#String)
Return
End

MySQL / SQL Incrementing a Column

Im trying to keep track of points / stats by making a column auto increment. However, it's not working as I want it. I want it to auto increment if the row gets updated, not if a new row gets added. For example, if I run the update command it will just add one to the "count" column for the row I updated. If I add a new row it'll start at 0!
Here is my code to create a table:
statement = connection.prepareStatement(
"CREATE TABLE IF NOT EXISTS stats" +
"(" +
"id varchar(100) not null," +
"count int not null auto_increment," +
"PRIMARY KEY (id)," +
"KEY (count)" +
")"
);
statement.execute();
Here is how I update to a specific row:
connection = plugin.getHikari().getConnection();
statement = connection.prepareStatement("INSERT INTO stats (id) VALUES(?) ON DUPLICATE KEY UPDATE id=?");
statement.setString(1, id.toString());
statement.setString(2, id.toString());
statement.execute();
Thanks,
- Nicster

Use Before update trigger in this case. Set default value to 1. and update/increment it by 1 on every update using trigger.

1) Remove the AUTO_INCREMENT attribute from the `count` column.
AUTO_INCREMENT isn't a suitable mechanism for what you are trying to achieve.
2) Add a DEFAULT 1 to the definition of the `count` column
When a new row is inserted into the table, and a value is not supplied for the `count` column, the default value will be assigned to the column.
3) re-write the INSERT statement to increment the `count` column when an attempt is made to add a duplicate `id` value
INSERT INTO atickets_stats (id)
VALUES ( ? )
ON DUPLICATE KEY
UPDATE count = count + 1 ;

From mysql doc (http://dev.mysql.com/doc/refman/5.7/en/example-auto-increment.html):
The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows
So you have to chose a different approach:
Read current value from database
Prepare your statement updating also the count value
Problem: Concurrency
You have to synchronize your method call to make it thread-safe.

I'm not sure why you're having that problem. You're close, IMHO. All you need to do is to make count as INT NOT NULL default 0. Then you should always do INSERT ON DUPLICATE KEY UPDATE like below:
CREATE TABLE IF NOT EXISTS atickets_stats (
`id` VARCHAR(100) NOT NULL,
`count` INT(11) UNSIGNED NOT NULL DEFAULT 0,
PRIMARY KEY (`id`)
);
INSERT INTO atickets_stats (id) VALUES(1) ON DUPLICATE KEY UPDATE count = count + 1;
Note, I changed the count column to be INT(11) UNSIGNED because I assume you won't ever store negative value here. You can take out UNSIGNED if you'll have negative value.

keep latest n entries in table

I have an sqlite database (on android) where I want to store the latest N entries of some data.
The primary key of the table is a date field. Basically whenever I insert some row after the threshold is reached, I want to delete the oldest entry from the table.
Is there any especially clever/nice way to do this? Note that I always check the invariant (nr rows <= THRESHOLD) after each insert so we don't have to deal with anything but with deleting the oldest entry.
What I'm planning to do is basically:
insert data
if count(*) of table <= THRESHOLD: goto 4
DELETE FROM table WHERE date == (SELECT date from table order by date ASC LIMIT 1);
DONE
Note I'm using ORMlite, but since there's no user data involved I can just use raw SQL, so there shouldn't be a problem.

DELETE FROM table WHERE date = (SELECT MAX(date) from table LIMIT 1);

You can use a trigger to delete the oldest row when a new row is added, and the number of rows is over your threshold.
The count of rows can be kept in a separate accounting table to avoid a COUNT on every insert.
Here's a complete example:
create table bookkeepings (bk_name text primary key, bk_value integer not null);
insert or replace into bookkeepings values ('Max Results', 50);
insert or replace into bookkeepings values ('Qty Results', 0);
create table results
(r_timestamp text primary key default (datetime(current_timestamp)),
result text);
create trigger results_limit_trigger before insert on results"
for each row"
when (select bk_value from bookkeepings where bk_name = 'Qty Results')
>= (select bk_value from bookkeepings where bk_name = 'Max Results')
begin
delete from results
where r_timestamp = (select r_timestamp from results order by r_timestamp limit 1);
end;
create trigger results_count_insert_trigger after insert on results
for each row
begin
update bookkeepings set bk_value = bk_value + 1 where bk_name = 'Qty Results';
end;
create trigger results_count_delete_trigger after delete on results
for each row
begin
update bookkeepings set bk_value = bk_value - 1 where bk_name = 'Qty Results';
end;

How about this?
-- keep the last N records by expiration date
declare #expDate datetime
set #expDate = (select top 100 max(dt) from table order by dt asc);
delete from table where dt > #expDate

Ordering by a max or a min from another table

I have a table that consists of a unique id, and a few other attributes. It holds "schedules". Then I have another table that holds a list of all the times each schedule has or will "fire". This isn't the exact schema, but it's close:
create table schedule (
id varchar(40) primary key,
attr1 int,
attr2 varchar(20)
);
create table schedule_times (
id varchar(40) foreign key schedule(id),
fire_date date
);
I want to query the schedule table, getting the attributes and the next and previous fire_dates, in Java, sometimes ordering on one of the attributes, but sometimes ordering on either previous fire_date or the next fire_date. Ordering by the attributes is easy, I just stick an "order by" into the string while I'm building my prepared statement. I'm not even sure how to go about selecting the last fire_date and the next one in a single query - I know that I can find the next fire_date for a given id by doing a
SELECT min(fire_date)
FROM schedule_times
WHERE id = ? AND
fire_date > sysdate;
and the similar thing for previous fire_date using max() and fire_date < sysdate. I'm just drawing a blank on how to incorporate that into a single select from the schedule so I can get both next and previous fire_date in one shot, and also how to order by either of those attributes.

You can do that using two sub-queries in Left Joins.
This has the advantage of returning NULL for your fire_dates if there is no next/previous schedule.
Select id, attr1, attr2, next_fire_date, previous_fire_date
From schedule s
Left Join ( Select id, Min(fire_date) As next_fire_date
From schedule_times st
Where st.fire_date > Sysdate
Group By id ) n
On ( n.id = s.id )
Left Join ( Select id, Max(fire_date) As previous_fire_date
From schedule_times st
Where st.fire_date < Sysdate
Group By id ) p
On ( p.id = s.id )
You can then add your ORDER BY on next_fire_date or previous_fire_date.
If performance matters, create a compound index on schedule_times( id, fire_date ), this will allow the sub-queries to read only from this index.

Try something like this:
select schedule.*,
(
select max(si.fire_date) from schedule_times si where si.id = schedule.id and si.fire_date < sysdate
) as prevfire,
(
select min(si.fire_date) from schedule_times si where si.id = schedule.id and si.fire_date > sysdate
) as nextfire
from schedule
where id = ?
order by attr1

Modify the query to
SELECT Distinct S.ID, ATTR1, ATTR2,
LEAD(FIRE_DATE, 1, SYSDATE) OVER (PARTITION BY S.ID ORDER BY S.ID) NEXT_FIRE_DATE,
LAG(FIRE_DATE, 1, SYADATE) OVER (PARTITION BY S.ID ORDER BY S.ID) PREV_FIRE_DATE
FROM SCHEDULE S,SCHEDULE_TIMES ST WHERE ST.ID=S.ID;
THIS WAS SIMPLE QUERY. YOU CAN TRY THIS.
LEAD has the ability to compute an expression on the next rows (rows which are going to come after the current row) and return the value to the current row. The general syntax of LEAD is shown below:
LEAD (sql_expr, offset, default) OVER (analytic_clause)
sql_expr is the expression to compute from the leading row.
offset is the index of the leading row relative to the current
row. offset is a positive integer
with default 1.
default is the value to return if the offset points to a row
outside the partition range.
The syntax of LAG is similar except that the offset for LAG goes into the previous rows.