I have the following table:
row_number itemID score
1 45 99
2 45 47
1 46 98
2 46 20
1 47 98
2 47 20
… … …
Which is the output of the following query:
SET #num := 0, #itemID_grouping := '';
SELECT row_number,
itemID,
score
FROM (SELECT itemID,
score,
#num := IF(#itemID_grouping = itemID, #num + 1, 1) AS row_number,
#itemID_grouping := itemID AS temp
FROM my_table
ORDER BY itemID,
score DESC) AS x
WHERE x.row_number <= 2;
From the following original table:
my_table:
itemID score
46 99
… …
So for each itemID, I have a set of two values (the two highest scores).
I'd like another column that contains 'y' or 1 if, for each set, the number with row_number=1 is greater than a certain threshold and the number with row_number=2 is lower than a certain threshold. Any ideas?
OK I found an answer (it might not be very fast but it does the job):
set #num := 0, #itemID_grouping := '',#num_temp:=0,#flag1:=0,#flag2:=0;
select row_number,itemID, score,flag2
from
(
select itemID,score,
#num := if(#itemID_grouping = itemID, #num + 1, 1) as row_number,
#flag1:= if(#num=1 AND score>90,1,0) as flag1,
#flag2:= if(#num=2 AND #flag_temp=1 AND score<70,1,0) as flag2,
#itemID_grouping := itemID as temp,
#flag_temp:=#flag1 as temp_flag
from my_table
order by itemID,score desc
) as x
where x.row_number <= 2;
Related
I have a table
Id Name Id_collection Price
1 good1 2 10
2 good2 1 101
3 good3 3 102
4 good4 2 10
5 good5 2 10
I need to Group By id_collection, but i need to show 2 rows (to be able to change this value via variable or ... Ex: to change to 3 or 4 )
not
1
2
3
Ex
1
1
2
2
3
3
or
Ex
1
1
1
2
2
2
3
3
3
so the result must be
Id Name Id_collection Price
1 good1 2 10
4 good4 2 10
2 good2 1 101
3 good3 3 102
I was thinking about procedure or loop, but i didn't that before, Please help!!!
You want to group by adjacent values . . . in MySQL. You can use variables to assign the group. Alternatively, you can use this method to assign the group: count the number of rows that have id_collection different from each row with a smaller id.
You don't specify how to calculate the other columns, but here is a guess:
select min(id) as id, min(name) as name, id_collection, avg(price) as price
from (select t.*,
(select count(*)
from t t2
where t2.id_collection <> t.id_collection and
t2.id < t.id
) as grp
from t
) t
group by id_collection, grp;
EDIT:
I just realized that you probably don't want to aggregate the results; you probably just want the first row. For that, use variables:
select t.*
from (select t.*,
(#rn := if(#id = id_collection, #rn,
if(#id := id_collection, #rn + 1, #rn + 1)
)
) as rn
from t cross join
(select #id = -1, #rn := 0) params
order by id
) t
where rn = 1;
I edited a little the answer which #Gordon_Linoff posted, and it works now, you just have to change rn <= 3 this number and will get the various results.
#Gordon_Linoff - Thank you, this really helped me
select t.*
from (select t.*,
(#rn := if(#id = id_collection, #rn + 1,
if(#id := id_collection, 1, 0)
)
) as rn
from t cross join
(select #id := -1, #rn := 0) params
order by id_collection
) t
where rn <= 3;
I have a below table and wants to select only last 2 entries of all users.
Source table:
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 10 2016-5-12
2 10 2016-5-12
1 11 2016-6-12
2 12 2016-8-12
3 12 2016-8-12
2 13 2016-8-12
1 14 2016-9-12
3 14 2016-9-12
3 11 2016-6-12
Expected output is like, (should list only recent 2 quizid entries for all users)
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 14 2016-9-12
1 11 2016-6-12
2 13 2016-8-12
2 12 2016-8-12
3 14 2016-9-12
3 12 2016-8-12
Any idea's to produce this output.
Using MySQL user defined variables you can accomplish this:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2
Working Demo
Note: If you want at most x number of entries for each user then change the condition in where clause like below:
WHERE t.row_number <= x
Explanation:
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC;
This query sorts all the data in ascending order of userId and descending order of quizendtime(AID).
Now take a walk on this (multi) sorted data.
Every time you see a new userId assign a row_number (1). If you see the same user again then just increase the row_number.
Finally filtering only those records which are having row_number <= 2 ensures the at most two latest entries for each user.
EDIT: As Gordon pointed out that the evaluation of expressions using user defined variables in mysql is not guaranteed to follow the same order always so based on that the above query is slightly modified:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF (
#sameUser = UserId,
#a := #a + 1,
IF(#sameUser := UserId, #a := 1, #a:= 1)
)AS row_number
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2;
WORKING DEMO V2
User-defined variables are the key to the solution. But, it is very important to have all the variable assignments in a single expression. MySQL does not guarantee the order of evaluation of expressions in a select -- and, in fact, sometimes processes them in different orders.
select t.*
from (select t.*,
(#rn := if(#u = UserId, #rn + 1,
if(#u := UserId, 1, 1)
)
) as rn
from t cross join
(select #u := -1, #rn := 0) params
order by UserId, quizendtime desc
) t
where rn <= 2;
I have table with 3 columns, now how find value if it appears next 3 times immediately
i.e 1st trnas_value appears in next 3 consecutive times (repeaded 4 times) and 2nd and 6th also rows also repeated the same.date column is sorted from A_Z
date tran_val name
23mar 22 mark
24mar 22 mark
25mar 22 mark
26mar 22 mark
27mar 22 mark
28jan 99 john
29jan 99 john
30jan 99 john
31jan 99 john
output
name trans_value consecutive_count
mark 22 2
john 99 1
we have a code which is not giving the above output..
SELECT name,
tran_val,
MAX(cnt - 3) AS consecutive_count
FROM
(
SELECT date,
tran_val,
name,
#cnt:=IF(#tran_val=tran_val AND #name=name, #cnt + 1, 1) AS cnt,
#tran_val:=tran_val,
#name:=name
FROM some_table
CROSS JOIN (SELECT #cnt:=0, #tran_val:=0, #name:='') sub0
ORDER BY `date`
) sub1
GROUP BY name,
tran_val
any modification in the above code which will get desired output.thanks
Try this:
SELECT `tran_val`, `name`, COUNT(*) - 3
FROM (
SELECT `date`, `tran_val`, `name`, rn - seq AS grp
FROM (
SELECT `date`, `tran_val`, `name`,
#rn := #rn + 1 AS rn,
#seq := IF(#name = `name` And #val = `tran_val`, #seq+1, 1) AS seq,
#name := name,
#val := tran_val
FROM mytable
CROSS JOIN (SELECT #rn := 0, #seq := 0, #name = '', #val = 0) AS vars
ORDER BY `date`) AS t ) AS s
GROUP BY `tran_val`, `name`, grp
HAVING COUNT(*) > 3
You need two separate variable to enumerate sequences:
#rn just enumerates consecutive table rows
#seq enumerates consecutive table rows having the same name, tran_val values.
The difference between these two variables, i.e. #rn - #seq, identifies islands of consecutive table rows having the same name, tran_val values.
Edit: I added a HAVING clause to the query so as to filter out islands having a population of 3 or less consecutive rows.
Demo here
I have a table table1 in mysql like this:
price item count
100 xyz 5
200 xyz 1
300 xyz 4
400 abc 1
500 abc 2
I want to insert a new column 'new_price' that will hold the 'price' for that 'item' with the highest 'count'. So the new table will be
price item count new_price
100 xyz 5 100
200 xyz 1 100
300 xyz 4 100
400 abc 1 500
500 abc 2 500
What is the most efficient way of doing this? Thanks very much for your help.
I think the easiest approach is to use variables:
select t.*,
(#price := if(#i = item, #price,
if(#i := item, price, price)
)
) as new_price
from table1 t cross join
(select #i := '', #price := -1) vars
order by item, count desc;
If you actually want to update values in the table, you can fit this into an update as well:
update table1 t join
(select t.*,
(#price := if(#i = item, #price,
if(#i := item, price, price)
)
) as new_price
from table1 t cross join
(select #i := '', #price := -1) vars
order by item, count desc
) tp
on tp.item = t.item and tp.price = t.price and tp.count = t.count
set t.new_price = tp.price;
This is my code and works for ties but it does not skip position on ties
SELECT `item`, (`totalrate` / `nrrates`),
#rank_count := #rank_count + (totalrate/nrrates < #prev_value) rank,
#prev_value := totalrate/nrrates avg
FROM table, (SELECT #prev_value := NULL, #rank_count := 1) init
ORDER BY avg DESC
Here is the out I get
item (`totalrate` / `nrrates`) rank avg
Virginia 10.0000 1 10
Ana 9.7500 2 9.75
Angeie 9.72 3 9.72
Carel 9.666666666 4 9.66
sammy 9.666666666 4 9.66
Oda 9.500000000 5 9.5
I want
item (`totalrate` / `nrrates`) rank avg
Virginia 10.0000 1 10
Ana 9.7500 2 9.75
Angeie 9.72 3 9.72
Carel 9.666666666 4 9.66
sammy 9.666666666 4 9.66
Oda 9.500000000 6 9.5
To skip the 5 position
I would like to merge with this that does skip position on ties
(I took the below code from this post
MySQL Rank in the Case of Ties)
SELECT t1.name, (SELECT COUNT(*) FROM table_1 t2 WHERE t2.score > t1.score) +1
AS rnk
FROM table_1 t1
how would I modify my code to get it to skip position with the above code it looks simple but i haven't figured it out.
Thanks
On ties, you may want to skip and use current row num to next unmatched avg value row as next rank.
Following should help you
SELECT `item`, #curr_avg := ( `totalrate` / `nrrates` )
, case when #prev_avg = #curr_avg then #rank := #rank
else #rank := ( #cur_row + 1 )
end as rank
, #cur_row := ( #cur_row + 1 ) as cur_row
, #prev_value := #curr_avg avg
FROM table
, ( SELECT #prev_avg := 0, #curr_avg := 0
, #rank := 0, #cur_row := 0 ) init
ORDER BY avg DESC
Similar examples:
To display top 4 rows using rank
Mysql Query for Rank (RowNumber) and Groupings
Update a field with an incrementing value that resets based on
field
Here's another alternative. First, the averages are calculated. If they are already available in a table, it would be even easier (as can be seen in the fiddle demo). Anyways, the rank is based on the logic of counting how many items have a lesser average than the current item.
SELECT
A1.`item`,
A1.avg,
COUNT(A2.`item`) avg_rank
FROM
(
SELECT `item`, (`totalrate` / `nrrates`),
#prev_value := totalrate/nrrates avg
FROM table, (SELECT #prev_value := NULL, #rank_count := 1) init
) A1 --alias for the inline view
INNER JOIN
(
SELECT `item`, (`totalrate` / `nrrates`),
#prev_value := totalrate/nrrates avg
FROM table, (SELECT #prev_value := NULL, #rank_count := 1) init
) A2 --alias for the inline view
ON A2.avg < A1.avg
GROUP BY A1.id, A1.avg
ORDER BY A1.avg;
SQL Fiddle demo