Oracle 18c

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CREATE TABLE people (ID, Name) AS
SELECT 1, 'John' FROM DUAL UNION ALL
SELECT 2, 'Ian' FROM DUAL UNION ALL
SELECT 3, 'Mike' FROM DUAL
3 rows affected

CREATE TABLE presentations(ID, Title) AS
SELECT 1, 'A new hope' FROM DUAL UNION ALL
SELECT 2, 'The Empire Strikes Back' FROM DUAL UNION ALL
SELECT 3, 'Return of the Jedi' FROM DUAL
3 rows affected

CREATE TABLE people_presentations(people_ID, presentation_ID) AS
SELECT 1, 1 FROM DUAL UNION ALL
SELECT 2, 1 FROM DUAL UNION ALL
SELECT 2, 2 FROM DUAL UNION ALL
SELECT 1, 3 FROM DUAL UNION ALL
SELECT 3, 3 FROM DUAL
5 rows affected

WITH cteAttendees
  AS (SELECT pp.PRESENTATION_ID,
             ',' || LISTAGG(pp.PEOPLE_ID, ',') WITHIN GROUP (ORDER BY pp.PEOPLE_ID) || ',' AS ATTENDEES
  FROM PEOPLE_PRESENTATIONS pp
  GROUP BY pp.PRESENTATION_ID)
SELECT *
  FROM cteAttendees
  WHERE ATTENDEES LIKE '%,1,%' AND
        ATTENDEES LIKE '%,2,%'


PRESENTATION_ID
ATTENDEES


1
,1,2,