There is a table(Course Interests) which has all the values in one cell. But those values are just ids and I want to join them with another table(Course) so I can know their names.
Course Interests:
MemberID MemberName CoursesInterested
-------------- --------------------- --------------
1 Al 1,4,5,6
2 A2 3,5,6
Course Table:
CourseId Course
-------------- ---------------------
1 MBA
2 Languages
3 English
4 French
5 Fashion
6 IT
Desired Output:
MemberID MemberName CoursesInterested
-------------- --------------------- --------------
1 Al MBA,French,Fashion,IT
2 A2 English,Fashion,IT
I would like to do a SQL query in MySql that can help me to extract the desired output. I know how to do it in the opposite way(join values to one cell), but I've struggling on seek a way to separate the ids and do a cross-join into another table.
I'll appreciate any help from the community. Thanks
Use FIND_IN_SET
to search for something in a comma-delimited list.
SELECT i.MemberID, i.MemberName, GROUP_CONCAT(c.Course) AS CoursesInterested
FROM CourseInterests AS i
JOIN Course AS c ON FIND_IN_SET(c.CourseId, i.CoursesInterested)
However, it would be better to create a relation table instead of storing the courses in a single column. This type of join cannot be optimized using an index, so it will be expensive for a large table.
Try this Out:
SELECT MemberID,MemberName,Group_Concat(C.Course) from
(
SELECT MemberID,MemberName,SUBSTRING_INDEX(SUBSTRING_INDEX(t.CoursesInterested, ',', n.n), ',', -1) value
FROM Table1 t CROSS JOIN
(
SELECT a.N + b.N * 10 + 1 n
FROM
(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
ORDER BY n
) n
WHERE n.n <= 1 + (LENGTH(t.CoursesInterested) - LENGTH(REPLACE(t.CoursesInterested, ',', '')))
ORDER BY MemberID,value
) T JOIN course C ON T.value = C.CourseId
Group By MemberID,MemberName
Output:
MemberID MemberName CoursesInterested
-------------- --------------------- --------------
1 Al MBA,French,Fashion,IT
2 A2 English,Fashion,IT
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