Find if two columns exist in another table, matched as a pair - sql

Question

I've seen some other questions about comparing multiple columns, but I'm not sure they fit this exact need.
I'm trying to ensure an exact pair of columns in one table exists as the exact same pair of columns in another table. The goal is to check and mark a bit column as true false if it exists.
The last part of this script returns a 1, but I'm not sure if the logic ensures the exact pair is in the second table.
Is the logic in the last part of the script comparing both tables correct?
Sample Data:
CREATE TABLE #t1
(
courseid VARCHAR(10)
,courseNumber VARCHAR(10)
)
INSERT INTO #t1(
courseid
, courseNumber
)
VALUES
(3386341, 3387691)
CREATE TABLE #t2
(
courseid VARCHAR(10)
,courseNumber VARCHAR(10)
,CourseArea VARCHAR(10)
,CourseCert VARCHAR(10)
,OtherCourseNum VARCHAR(10)
)
INSERT INTO #t2(
courseid
, courseNumber
, CourseArea
, CourseCert
, OtherCourseNum
)
VALUES
(3386341 , 3387691 , 9671 , 9671 , 233321)
,(3386341 , 3387691 , 9671 , 9671 , 233321)
,(3386342 , 3387692 , 9672 , 9672 , 233322)
,(3386342 , 3387692 , 9672 , 9672 , 233322)
,(3386343 , 3387693 , 9673 , 9673 , 233323)
,(3386343 , 3387693 , 9673 , 9673 , 233323)
SELECT
CASE WHEN courseid IN (SELECT courseid FROM #t1) AND courseNumber IN (SELECT courseNumber FROM #t2) THEN 1 ELSE 0 END AS IsCourse
FROM #t1

Answer 1

I would always opt for an exists correlation here as it's faster and NULL-safe
select
case when exists (
select * from #t2 t2
where t2.courseid = t1.courseId and t2.courseNumber = t1.courseNumber
) then 1 else 0 end IsCourse
from #t1 t1;

Answer 2

No, your query doesn't correlate the id & number so your query will return a positive if the id exists anywhere in t2 and the number exists anywhere in t2, but doesn't confirm they exist on the same row. You want EXISTS e.g.
SELECT
CASE WHEN EXISTS (
SELECT 1
FROM #t2 t2
WHERE t2.courseid = t1.courseid
AND t2.courseNumber = t1.courseNumber
) THEN 1 ELSE 0 END AS IsCourse
FROM #t1 t1;