How to give " Only in " condition in SQL? - mysql

Question

I have a table that has columns Name, Series and Season.
Name
series
season
abc
alpha
s1
abc
alpha
s2
pqr
alpha
s1
xyz
beta
s2
xyz
gamma
s3
abc
theta
s1
I am trying to extract the number of people who have watched only the series 'alpha', and not any other series.
How to get this count?
On giving the "where series='alpha' " condition, I get the counts of people who watched alpha, but not the counts of those who watched only alpha eg: abc has watched alpha as well as theta, but pqr has watched only alpha.

Answer 1

You could use a subquery to get only the names which have watched only distinct series and then filter in the where condition your specific serie
select count(yt.name) as only_alpha
from yourtable yt
inner join ( select name
from yourtable
group by name
having count(distinct series) = 1
) yt1 on yt.name=yt1.name
where yt.series='alpha';
https://dbfiddle.uk/n0PavP4H

Answer 2

You can use subquery, like this:
SELECT COUNT(DISTINCT name)
FROM t
WHERE name NOT IN (
SELECT DISTINCT name
FROM t
WHERE series<>'alpha'
) AND series='alpha'

Answer 3

If you really want to get the number of such people only, without their name or any further information, you can use a NOT EXISTS clause like this:
SELECT COUNT(*) AS desiredColumnName
FROM yourtable y
WHERE series = 'alpha'
AND NOT EXISTS
(SELECT 1 FROM yourtable y1 WHERE y.name = y1.name AND series <> 'alpha');
Thus, you can set your condition the person must not appear in any other series but the 'alpha' one.
If the same name can occur in different seasons, you can add a DISTINCT to count them only once. This should only be done if really required because it can slow down the query:
SELECT COUNT(DISTINCT name) AS desiredColumnName
FROM yourtable y
WHERE series = 'alpha'
AND NOT EXISTS
(SELECT 1 FROM yourtable y1 WHERE y.name = y1.name AND series <> 'alpha');
If your description is incorrect and you need also other information, you might do better with a GROUP BY clause etc.
Try out here: db<>fiddle

Answer 4

You can use like below
select sum(Record) as Count from (select count() as Record from yourtable where series='alpha'
group by series,name having count()=1) as data
Check below link
https://dbfiddle.uk/1Y3WZT23

Answer 5

I added some new cases to your table to see other anomalies that can happen. This is how it looks like now:
Name
series
season
abc
alpha
s1
abc
alpha
s2
abc
theta
s1
fgh
alpha
s1
fgh
alpha
s2
klj
gamma
s1
klj
gamma
s2
klj
gamma
s3
pqr
alpha
s1
xyz
beta
s2
xyz
gamma
s3
I maybe overcomplicated, but it can provide the correct result for your problem; you just need to COUNT() it. I tested other SQL queries under your question on my this table, but not all of them showed the correct figure. I doesn't recommend to use NOT IN ( sub query ) for the following reasons:
Strange results when running SQL IN and NOT IN using Redshift
Optimization for Large IN Lists
Consider using EXISTS instead of IN with a subquery
Please find my code here:
WITH helper_table as
(
SELECT "Name",
series,
count(1) as seasons_watched
FROM your_table
GROUP BY 1, 2
)
------------------------------------------------------------
SELECT t1."Name"
FROM
(
SELECT "Name",
count(1) as is_watched_at_least_one_series_of_alpha
FROM helper_table
WHERE series = 'alpha'
GROUP BY 1
) t1
INNER JOIN
(
SELECT "Name",
count(1) as watched_exactly_one_series_so_far
FROM helper_table
GROUP BY 1
HAVING count(1) = 1
) t2
ON t2."Name" = t1."Name"
;
Hope it helps!