How to get what percentage of total users joined what number of meetings in PostgreSQL? - sql

Question

There are two tables, one is called "user_preference" that contains all users:
id | firstname | lastname | email |
And "match" which combines users with meetups they joined:
id | matcher | partner | meetup |
Both matcher and partner are foreign keys that represent user_preference.id, meaning that same user can be both matcher and a partner in the same meetup.
What I need to know is what percentage of total unique users joined what number of meetings.
For example:
17% of users joined 5 meetups
20% of users joined 3 meetups
40% of users joined 1 meetup
23% of users joined 0 meetups
The number of meetups should not be hardcoded but dynamic.
But I want to avoid duplication of users for a single meetup and count them only once. For example this:
id | matcher | partner | meetup |
1 | user1 | user2 | meetup1 |
2 | user1 | user3 | meetup1 |
3 | user5 | user1 | meetup1 |
4 | user6 | user1 | meetup2 |
Should count that user1 visited only 2 meetups.
What I managed to do so far is to display the count of meetups each user visited but that is not what I need:
SELECT distinct up.email users, COUNT(m.user) meetups
FROM user_preference up
LEFT JOIN
(
SELECT matcher AS user FROM match
UNION ALL
SELECT partner AS user FROM match
) m ON m.user = up.id
GROUP BY up.email
ORDER BY meetups desc;

Answer 1

In the end I did this by making simple queries and looping through them in the code, its far from elegant solution but it should work.
If someone posts SQL solution I will accept and upvote it...
export const getDevStats = async () => {
const users = await getRepository(UserPreference).query(
`SELECT * FROM user_preference;`
);
const meetups = await getRepository(Meetup).query(
`SELECT * FROM meetup;`
);
const matches = await getRepository(Match).query(
`SELECT * FROM match;`
);
let userMatches: any = {};
users.forEach((user: any) => {
userMatches[user.id] = []
matches.forEach((match: any) => {
if(user.id == match.matcher || user.id == match.partner) {
if(userMatches[user.id].indexOf(match.meetup) === -1) {
userMatches[user.id].push(match.meetup);
}
}
});
});
let matchStats: any = {};
for (var userId of Object.keys(userMatches)) {
if (typeof matchStats[userMatches[userId].length] === 'undefined') {
matchStats[userMatches[userId].length] = 0;
}
matchStats[userMatches[userId].length]++;
}
return {
users: users,
meetups: meetups,
matches: matches,
userMatches: userMatches,
matchStats: matchStats
};
};