I have a query which works great given that the result is only one number, but now I need to allow for multiple rows to be returned and the query cannot handle that because it uses a user define variable... here is original procedure
CREATE DEFINER=`root`#`%` PROCEDURE `MapRank`(pTankID bigint,pMapID int, pColor int(2))
BEGIN
SET #RankNumber:=0;
select RankNumber
from
(select
TankID,
#RankNumber:=#RankNumber+1 as RankNumber,
MapID,
Color
from MAPDATA WHERE MapID = pMapID order by Rank DESC, TotalPP DESC) Query1 where TankID = pTankID AND COLOR = pColor ;
END
this returns a single number, essentially counting the number of records down it is, giving me the "row" location.
now I need to change it to give me all rows with out the where for mapid and color, so that I can see all ranks for all mapid/color combo
this is what I have that currently does not work
SET #RankNumber:=0;
select
RankNumber,MapID,COlor
from
(select
TankID,
#RankNumber:=#RankNumber + 1 as RankNumber,
MapID,
Color
from
MAPDATA
order by TotalPP DESC) Query1
where
TankID = 18209 ORDER BY RankNumber
the yielding query result looks as such:
1062 3 1
3544 3 0
6717 17 1
6752 17 3
7453 3 2
7860 17 0
7984 17 2
9220 3 3
if I run manually lets say, map id 3 and color 3 which says rank number is 9220 with the FIRST query I get this
6022
I need this to be able to be done possibly from multiple MySQL connections so ideally done without use of a temporary variable since its possible another person may come in and use that... any help would be great.
After digging and messing more I have found the solution to be to set the variable back to zero from within the outer select.. and since user defined variable are connection level and I utilize pooling we should never have an issue.
SET #RankNumber:=0;
select
RankNumber,MapID,COlor, #RankNumber:=0
from
(select
TankID,
#RankNumber:=#RankNumber + 1 as RankNumber,
MapID,
Color
from
MAPDATA
order by MapID, Rank DESC, TotalPP DESC ) Query1
where
TankID = pTankID ORDER BY RankNumber;
Related
I am trying to write a quarry in a module for Dolibarr ERP. But module hase a part of code that is predefined and can not be changed. And I need to insert a SUM() function in it that will combine rows with similar id. That i know how to do in a regular MySQL:
SELECT fk_product AS prod, SUM(value) AS qty
FROM llx_stock_mouvement
WHERE type_mouvement = 2 AND label LIKE 'SH%'
GROUP BY fk_product
ORDER BY 1 DESC
LIMIT 26
that gives me what I want :
prod qty
1 13
2 10
BUT module has a predefined unchangeable code :
this part is predefined module writes it himself based on values provider in it:
SELECT DISTINCT
c.fk_product AS com,
c.value AS qty
THIS PART I CAN WRITE IN A MODULES GUI:
FROM
llx_stock_mouvement AS c
WHERE
type_mouvement = 2
AND label LIKE 'SH%'
And this part is predefined:
ORDER BY 1 DESC
LIMIT 26
I would appreciate any help and advice on question is there any workaround that can be done to make my desired and result ampere ? As it would using the first code I posted ?
If you can only modify the bit in the middle box then you might need to use a subquery;
--fixed part
SELECT DISTINCT
c.fk_product AS com,
c.value AS qty
--begin your editable part
FROM
(
SELECT fk_product,
SUM(value) AS value
FROM llx_stock_mouvement
WHERE type_mouvement = 2 AND label LIKE 'SH%'
GROUP BY fk_product
) c
--end your editable part
--fixed part
ORDER BY 1
DESC
LIMIT 26
I have a few tables that have millions of records where a sensor was sending multiple 0 and 1 values and this data was logged to the table even though we only needed it to keep the very first 1 or 0 per each 1 to 0 or 0 to 1 change.
Adjustments have been made so we only now get the 1 and 0 values on each change and not every one second or whatever but I need to cleanup the unnecessary records from the tables.
I've done some research and testing and I'm having trouble figuring out what method to use here to delete the records not needed. I was trying to figure out how to retain the previous value record using variables and also created row numbers but it's not working as I need it to.
I created an SQLFiddle here and tried some logic per the example post MySQL - How To Select Rows Depending on Value in Previous Row (Remove Duplicates in Each Sequence). I keep getting back no results from this and when I tried running it on a large local MySQL table, and I got an error wto I have to increase the MySQL Workbench read query timeout to 600 or it lost connection.
I also found the "MySql - How get value in previous row and value in next row?" post and tried some variations of it and also "How to get next/previous record in MySQL?" and I've come up with total failure getting the expected results.
The Data
The data in the tables has a TimeStr column and a Value column just as in the screen shot and on the SQLFiddle link I posted with a small sample of the data.
Each record will never have the same TimeStr value but I really only need to keep the very first record time wise when the sensor either turned ON or OFF if that clarifies.
I'm not sure if the records will need an incremental row number added to get the expected results since it only has the TimeStr and the Value records otherwise.
My Question
Can anyone help me determine a method that I can use on a couple large tables to delete the records from a table where there are subsequent and duplicate Value values so the tables only has the very first 1 or 0 records where those actually change from a 1 to 0 or 0 to 1?
I will accept an answer that also results in just the records needed—but any that perform fast would be even more greatly appreciated.
I can easily put those into a temp table, drop the original table, and then create and insert the needed records only into the original table.
Expected Results
| TimeStr | Value |
|----------------------|-------|
| 2018-02-13T00:00:00Z | 0 |
| 2018-02-13T00:00:17Z | 1 |
| 2018-02-13T00:00:24Z | 0 |
| 2018-02-13T00:00:28Z | 1 |
Select t.timestr, t.value from (
SELECT s.*, #pv x1, (#pv := s.value) x2
FROM sensor S, (select #pv := -1) x
ORDER BY TimeStr ) t
where t.x1 != t.x2
See http://sqlfiddle.com/#!9/8d0774/122
Try this :
SET #rownum = 0;
SET #rownum_x = 0;
SELECT b.rownum, b.TimeStr, b.Value
FROM
(
SELECT #rownum := #rownum+1 as rownum, TimeStr, Value
FROM sensor
ORDER BY TimeStr
) b
LEFT JOIN (
SELECT #rownum_x := #rownum_x+1 as rownum_x, TimeStr as TimeStr_x, Value as Value_x
FROM sensor
ORDER BY TimeStr
) x ON b.rownum = x.rownum_x + 1
where b.Value <> x.Value_x or x.Value_x is null
order by b.TimeStr
The result I got is
You want the first record for each value when it appears. This suggests variables. Here is one way that only involves sorting and no joining:
select t.*
from (select t.*,
(case when value = #prev_value then value
when (#save_prev := #prev_value) = NULL then NULL
when (#prev_value := value) = NULL then NULL
else #save_prev
end) as prev_value
from (select t.*
from sensor t
order by timestr
) t cross join
(select #prev_value := -1) params
) t
where prev_value <> value;
Notes:
The subquery for ordering only seems to be needed since MySQL 5.7.
The case is just a way to introduce serialized code. When using a variable it should only be used on one expression.
This only requires one sort -- and if you have an index, that doesn't even need to be a sort.
Here is a SQL Fiddle.
I've got a table:
player_id|player_name|play_with_id|play_with_name|
I made this table for a game.
Everyone who wants to play can sign up to it.
When they sign up the table stores player_id and player_name
When the period while they can sign up expires I want to assign every player_name to a play_with_name randomly.
So for example.. my structure would like this when they in sign up period:
player_id|player_name|play_with_id|play_with_name|
1 someone1
2 someone2
3 someone3
4 someone4
5 someone5
And this when the period expires:
player_id|player_name|play_with_id|play_with_name|
1 someone1 2 someone2
2 someone2 1 someone1
3 someone3 4 someone4
4 someone4 3 someone3
5 someone5 - -
I can't test this since I don't have a MySQL database handy and SQLFiddle seems to take forever to run anything, but this hopefully gets you there or at least close:
SET #row_num = 0;
SET #last_player_id = 0;
UPDATE P
SET
play_with_id =
CASE
WHEN P.player_id = SQ.player_id THEN SQ.last_player_id
ELSE player_id
END
FROM
Players P
LEFT OUTER JOIN
(
SELECT
#row_num := #row_num + 1 row_num,
#last_player_id last_player_id,
#last_player_id := player_id player_id
FROM
Players
WHERE
MOD(#row_num, 2) = 0
ORDER BY
RAND()
) SQ ON SQ.player_id = P.player_id OR SQ.last_player_id = P.player_id
The code (hopefully) sorts the players randomly then it pairs them based on that order. Every other player in the randomly sorted result is paired with the person right before them.
In MS SQL Server RAND() would only be evaluated once here and wouldn't end up affecting the ORDER BY, but I think that MySQL handles RAND() differently and generates a new value for each row in the result set.
I'm not sure why some client code isn't doing this as opposed to having this operation be done at the database level, but I suppose if you get the strategy for retrieving a randomized row set based on your DB from here, you could then write a stored procedure with a cursor or iterator to loop through the result set of something like:
select player_id, player_name from players order by RAND()
and then loop through the all the table rows to update the play_with_id and play_with_name, where the previously selected player_id <> play_with_id.
I am trying to give different cities a "score" from 1 to 5 based on multiple different criteria to eventually add up the scores and make a decision about which city is the best.
The table "international_tobacco_alcohol" contains values of the percentage of income that residents spend on alcohol and tobacco. I want to sort the results into 5 bins where 1 is the lowest percentage spending, 5 is the highest.
I added a "sort_order" column
ALTER TABLE international_tobacco_alcohol ADD COLUMN sort_order INT DEFAULT NULL;
SET #x = 0;
UPDATE international_tobacco_alcohol SET sort_order = (#x:=#x+1)
ORDER BY spent_on_alcohol_and_tobacco;
SELECT * FROM international_tobacco_alcohol;
And then I wanted to add the column "score" but I don't know how to do it correctly. I have tried basically every variation I can think of:
ALTER TABLE international_tobacco_alcohol ADD COLUMN score INT DEFAULT NULL;
UPDATE international_tobacco_alcohol
SET score = CASE
WHEN sort_order < .2*MAX(sort_order) THEN 1
WHEN sort_order=> .2*MAX(sort_order)and <.4*MAX(sort_order) THEN 2
WHEN sort_order=> .4*MAX(sort_order)and <.6*MAX(sort_order) THEN 3
WHEN sort_order=> .6*MAX(sort_order)and <.8*MAX(sort_order) THEN 4
WHEN sort_order=> .8*MAX(sort_order)and =<MAX(sort_order) THEN 5
END;
I want the CASE WHEN clause to be in proportion to the total number of rows, not a predefined value, so that it can be recreatable and used with new data.
I appreciate some help. If I could create the score without the intermediate step of creating the "sort_order" column that would be great too.
`
You don't need the [sort_order] by [spent_on_alcohol_and_tobacco].
An alternative is to use RANK() function or DENSE_RANK();
I don't know the columns but you can do something like this:
SELECT [col_1], [col_2]
,RANK() OVER
(PARTITION BY [Location] ORDER BY [spent_on_alcohol_and_tobacco] DESC) AS Rank
FROM [international_tobacco_alcohol]
Hope this helps
Let's say I have a list of values, like this:
id value
----------
A 53
B 23
C 12
D 72
E 21
F 16
..
I need the top 10 percent of this list - I tried:
SELECT id, value
FROM list
ORDER BY value DESC
LIMIT COUNT(*) / 10
But this doesn't work. The problem is that I don't know the amount of records before I do the query. Any idea's?
Best answer I found:
SELECT*
FROM (
SELECT list.*, #counter := #counter +1 AS counter
FROM (select #counter:=0) AS initvar, list
ORDER BY value DESC
) AS X
where counter <= (10/100 * #counter);
ORDER BY value DESC
Change the 10 to get a different percentage.
In case you are doing this for an out of order, or random situation - I've started using the following style:
SELECT id, value FROM list HAVING RAND() > 0.9
If you need it to be random but controllable you can use a seed (example with PHP):
SELECT id, value FROM list HAVING RAND($seed) > 0.9
Lastly - if this is a sort of thing that you need full control over you can actually add a column that holds a random value whenever a row is inserted, and then query using that
SELECT id, value FROM list HAVING `rand_column` BETWEEN 0.8 AND 0.9
Since this does not require sorting, or ORDER BY - it is O(n) rather than O(n lg n)
You can also try with that:
SET #amount =(SELECT COUNT(*) FROM page) /10;
PREPARE STMT FROM 'SELECT * FROM page LIMIT ?';
EXECUTE STMT USING #amount;
This is MySQL bug described in here: http://bugs.mysql.com/bug.php?id=19795
Hope it'll help.
I realize this is VERY old, but it still pops up as the top result when you google SQL limit by percent so I'll try to save you some time. This is pretty simple to do these days. The following would give the OP the results they need:
SELECT TOP 10 PERCENT
id,
value
FROM list
ORDER BY value DESC
To get a quick and dirty random 10 percent of your table, the following would suffice:
SELECT TOP 10 PERCENT
id,
value
FROM list
ORDER BY NEWID()
I have an alternative which hasn't been mentionned in the other answers: if you access from any language where you have full access to the MySQL API (i.e. not the MySQL CLI), you can launch the query, ask how many rows there will be and then break the loop if it is time.
E.g. in Python:
...
maxnum = cursor.execute(query)
for num, row in enumerate(query)
if num > .1 * maxnum: # Here I break the loop if I got 10% of the rows.
break
do_stuff...
This works only with mysql_store_result(), not with mysql_use_result(), as the latter requires that you always accept all needed rows.
OTOH, the traffic for my solution might be too high - all rows have to be transferred.