SQL Server 2019

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Microsoft SQL Server 2019 (RTM-CU6) (KB4563110) - 15.0.4053.23 (X64) 
 Jul 25 2020 11:26:55 
 Copyright (C) 2019 Microsoft Corporation
 Express Edition (64-bit) on Windows Server 2019 Standard 10.0 <X64> (Build 17763: ) (Hypervisor)



CREATE TABLE person (
  id int,
  name nvarchar(10)
);
insert into person (id, name) values
(1, 'Alice'),
(2, 'Bob'),
(3, 'Charlie'),
(4, 'David'),
(5, 'Eric')
;
5 rows affected

CREATE TABLE meeting (
  id int,
  title nvarchar(30)
);
insert into meeting (id, title) values
(100, 'Corporate training'),
(200, 'Weekly sales'),
(300, 'Welcome introduction'),
(400, 'Evaluation'),
(500, 'Missing Meeting')
;
5 rows affected

CREATE TABLE participant (
  idMeeting int,
  idPerson int
);
insert into participant (idMeeting, idPerson) values
(100,1), (100,2), (100,3), (100,4), (100,5),
(200,1), (200,2),
         (300,2), (300,3), (300,4),
                  (400,3),          (400,5),
                  (500,3),          (500,5)
;
14 rows affected

WITH cte AS (
        SELECT pe1.name as p1
             , pe2.name as p2
             , COUNT(*) AS cnt
             , MAX(COUNT(*)) OVER () AS max_cnt
          FROM participant pa1
          JOIN participant pa2
            ON pa2.idMeeting = pa1.idMeeting
           AND pa2.idPerson  > pa1.idPerson
          JOIN person pe1 on pe1.id = pa1.idPerson
          JOIN person pe2 on pe2.id = pa2.idPerson
         GROUP BY pe1.name, pe2.name
     )
SELECT *
  FROM cte
 WHERE cnt = max_cnt
;


p1
p2
cnt
max_cnt


Charlie
Eric
3
3


WITH cte AS (
        SELECT pe1.name as p1
             , pe2.name as p2
             , COUNT(*) AS cnt
             , MAX(COUNT(*)) OVER () AS max_cnt
          FROM participant pa1
          JOIN participant pa2
            ON pa2.idMeeting = pa1.idMeeting
           AND pa2.idPerson  > pa1.idPerson
          JOIN person pe1 on pe1.id = pa1.idPerson
          JOIN person pe2 on pe2.id = pa2.idPerson
          JOIN meeting  m on m.id   = pa1.idMeeting
         GROUP BY pe1.name, pe2.name
     )
SELECT *
  FROM cte
 WHERE cnt = max_cnt
;


p1
p2
cnt
max_cnt


Charlie
Eric
3
3


WITH cte AS (
        SELECT pa1.idPerson as p1
             , pa2.idPerson as p2
             , COUNT(*) AS cnt
             , MAX(COUNT(*)) OVER () AS max_cnt
          FROM participant pa1
          JOIN participant pa2
            ON pa2.idMeeting = pa1.idMeeting
           AND pa2.idPerson  > pa1.idPerson
         GROUP BY pa1.idPerson, pa2.idPerson
     )
SELECT *
  FROM cte
 WHERE cnt = max_cnt
;


p1
p2
cnt
max_cnt


3
5
3
3