SQL query with CASE statement ,multiple variables and sub variables - sql

Question

i am working on dataset where i need to write an query for below requirement either in R-programming or SQLDF , i want to know and learn to write in both language ( SQL and R ) ,kindly help.
Requirement is : i need to print Variable "a" from table when
Total_Scores of id 34 and Rank 3 is GREATER THAN Total_Scores of id 34 and Rank 4 else Print Variable b .
This above case Applicable for each id and Rank
id Rank Variable Total_Scores
34 3 a 11
34 4 b 6
126 3 c 15
126 4 d 18
190 3 e 9
190 4 f 10
388 3 g 20
388 4 h 15
401 3 i 15
401 4 x 11
476 3 y 11
476 4 z 11
536 3 p 15
536 4 q 6
i have tried to write SQL CASE statement and i am stuck ,could you please
help to write the query
"select id ,Rank ,
CASE
WHEN (select Total_Scores from table where id == 34 and Rank == 3) > (select Total_Scores from table where id == 34 and Rank == 4)
THEN "Variable is )
Final output Should be :
id Rank Variable Total_Scores
34 3 a 11
126 4 d 18
190 4 f 10
388 3 g 20
401 3 i 15
536 3 p 15

Answer 1

You seem to want the row with the highest score for each id. A canonical way to write this in SQL uses row_number():
select t.*
from (select t.*,
row_number() over (partition by id order by score desc) as seqnum
from t
) t
where seqnum = 1;
This returns one row per id, even when the scores are tied. If you want all rows in that case, use rank() instead of row_number().
An alternative method can have better performance with an index on (id, score):
select t.*
from t
where t.score = (select max(t2.score) from t t2 where t2.id = t.id);

Answer 2

You can try this.
SELECT T.* FROM (
SELECT id,
MAX(Total_Scores) Max_Total_Scores
FROM MyTable
GROUP BY id
HAVING MAX(Total_Scores) > MIN(Total_Scores) ) AS MX
INNER JOIN MyTable T ON MX.id = T.id AND MX.Max_Total_Scores = T.Total_Scores
ORDER BY id
Sql Fiddle

Answer 3

In R
library(dplyr)
df %>% group_by(id) %>%
filter(Total_Scores == max(Total_Scores)) %>% filter(n()==1) %>%
ungroup()
# A tibble: 6 x 4
id Rank Variable Total_Scores
<int> <int> <chr> <int>
1 34 3 a 11
2 126 4 d 18
3 190 4 f 10
4 388 3 g 20
5 401 3 i 15
6 536 3 p 15
Data
df <- read.table(text="
id Rank Variable Total_Scores
34 3 a 11
34 4 b 6
126 3 c 15
126 4 d 18
190 3 e 9
190 4 f 10
388 3 g 20
388 4 h 15
401 3 i 15
401 4 x 11
476 3 y 11
476 4 z 11
536 3 p 15
536 4 q 6
",header=T, stringsAsFactors = F)

Answer 4

Assuming that what you want is to get the subset of rows whose Total_Scores is largest for that id here are two approaches.
The question did not discuss how to deal with ties. There is one id in the example that has a tie but there is no output corresponding to it which I assume was not intendedand that either both the rows should have been output or one of them. Anyways in the solutions below in (1) it will give one of the rows arbitrarily if there are duplicates whereas (2) will give both.
1) sqldf
If you use max in an SQLite select it will automatically select the other variables of the same row so:
library(sqldf)
sqldf("select id, Rank, Variable, max(Total_Scores) Total_Scores
from DF
group by id")
giving:
id Rank Variable Total_Scores
1 34 3 a 11
2 126 4 d 18
3 190 4 f 10
4 388 3 g 20
5 401 3 i 15
6 476 3 y 11
7 536 3 p 15
2) base R In base R we can use ave and subset like this:
subset(DF, ave(Total_Scores, id, FUN = function(x) x == max(x)) > 0)
giving:
id Rank Variable Total_Scores
1 34 3 a 11
4 126 4 d 18
6 190 4 f 10
7 388 3 g 20
9 401 3 i 15
11 476 3 y 11
12 476 4 z 11
13 536 3 p 15
Note
The input in reproducible form:
Lines <- "id Rank Variable Total_Scores
34 3 a 11
34 4 b 6
126 3 c 15
126 4 d 18
190 3 e 9
190 4 f 10
388 3 g 20
388 4 h 15
401 3 i 15
401 4 x 11
476 3 y 11
476 4 z 11
536 3 p 15
536 4 q 6"
DF <- read.table(text = Lines, header = TRUE, as.is = TRUE)