SQL for selecting values in a single column by 'AND' condition - sql

Question

I have a table data like bellow
PersonId
Eat
111
Carrot
111
Apple
111
Orange
222
Carrot
222
Apple
333
Carrot
444
Orange
555
Apple
I need an sql query which return the total number of PersonId's who eat both Carrot and Apple.
In the above example the result is, Result : 2. (PersonId's 111 and 222)
An ms-sql query like 'select count(distinct PersonId) from Person where Eat = 'Carrot' and Eat = 'Apple''

Answer 1

You can actually get the count without using a subquery to determine the persons who eat both. Assuming that the rows are unique:
select ( count(distinct case when eat = 'carrot' then personid end) +
count(distinct case when eat = 'apple' then personid end) -
count(distinct personid)
) as num_both
from t
where eat in ('carrot', 'apple')

Answer 2

SELECT PersonID FROM Person WHERE Eat = 'Carrot'
INTERSECT
SELECT PersonID FROM Person WHERE Eat = 'Apple'

Answer 3

You can use conditional aggregation of a sort:
select
personid
from <yourtable>
group by
personid
having
count (case when eat = 'carrot' then 1 else null end) >= 1
and count (case when eat = 'apple' then 1 else null end) >= 1

Answer 4

At this example, I use STRING_AGG to make easy the count and transform 'Apple' and 'Carrot' to one string comparison:
create table #EatTemp
(
PersonId int,
Eat Varchar(50)
)
INSERT INTO #EatTemp VALUES
(111, 'Carrot')
,(111, 'Apple')
,(111, 'Orange')
,(222, 'Carrot')
,(222, 'Apple')
,(333, 'Carrot')
,(444, 'Orange')
,(555, 'Apple')
SELECT Count(PersonId) WhoEatCarrotAndApple FROM
(
SELECT PersonId,
STRING_AGG(Eat, ';')
WITHIN GROUP (ORDER BY Eat) Eat
FROM #EatTemp
WHERE Eat IN ('Apple', 'Carrot')
GROUP BY PersonId
) EatAgg
WHERE Eat = 'Apple;Carrot'

Answer 5

You can use EXISTS statements to achieve your goal. Below is a full set of code you can use to test the results. In this case, this returns a count of 2 since PersonId 111 and 222 match the criteria you specified in your post.
CREATE TABLE Person
( PersonId INT
, Eat VARCHAR(10));
INSERT INTO Person
VALUES
(111, 'Carrot'), (111, 'Apple'), (111, 'Orange'),
(222, 'Carrot'), (222, 'Apple'), (333, 'Carrot'),
(444, 'Orange'), (555, 'Apple');
SELECT COUNT(DISTINCT PersonId)
FROM Person AS p
WHERE EXISTS
(SELECT 1
FROM Person e1
WHERE e1.Eat = 'Apple'
AND p.PersonId = e1.PersonId)
AND EXISTS
(SELECT 1
FROM Person e1
WHERE e1.Eat = 'Carrot'
AND p.PersonId = e1.PersonId);
EXISTS statements have a few advantages:
No chance of changing the granularity of your data since you aren't joining in your FROM clause.
Easy to add additional conditions as needed. Just add more EXISTS statements in your WHERE clause.
The condition is cleanly encapsulated in the EXISTS, so code intent is clear.
If you ever need complex conditions like existence of a value in another table based on specific filter conditions, then you can easily add this without introducing table joins in your main query.
Some alternative solutions such as PersonId IN (SUBQUERY) can introduce unexpected behavior in certain conditions, particularly when the subquery returns a NULL value.

Answer 6

select
count(PersonID)
from Person
where eat = 'Carrot'
and PersonID in (select PersonID
from Person
where eat = 'Apple');
Only selecting those persons who eat apples, and from that result select all those that eat carrots too.

Answer 7

SELECT COUNT (A.personID) FROM
(SELECT distinct PersonID FROM Person WHERE Eat = 'Carrot'
INTERSECT
SELECT distinct PersonID FROM Person WHERE Eat = 'Apple') as A