MySQL Fetch Result Using Multiple Joins in one query? - mysql

Question

I have below tables
tbl_user
uid first_name last_name email_id
1 steve martin steve1#gmail.com
2 mark lee mark1#gmail.com
3 nelson wise nelson23#gmail.com
tbl_tier
tier_id tier_name points_required
1 Silver 100
2 Gold 200
3 Platinum 300
tbl_tier_earned
id tier_id uid
1 1 1
2 2 1
3 3 1
4 1 2
5 2 2
6 1 3
I need unique users with their current tiers like:
first_name last_name email_id current_tier
steve martin steve1#gmail.com Platinum
mark lee mark1#gmail.com Gold
I have tried below query but it gives me only 1 result:
SELECT u.first_name,u.last_name,u.email_id, t.tier_name
FROM tbl_tier_earned AS tte
INNER JOIN tbl_user AS u
ON u.uid = tte.uid
INNER JOIN tbl_tier AS t
ON tte.tier_id = t.tier_id
WHERE u.email_id!=""
ORDER BY t.points_required DESC LIMIT 0,1
How can I retrieve above data using mysql query?

Answer 1

It appears that the current tier is given by the max tier_id in the tbl_tier_earned table, for each user. One approach here would be to join the user table to a subquery on the tbl_tier_earned table which finds the max tier.
SELECT
u.first_name,
u.last_name,
u.email_id,
COALESCE(t2.tier_name, 'NA') AS current_tier
FROM tbl_user u
LEFT JOIN
(
SELECT uid, MAX(tier_id) AS max_tier_id
FROM tbl_tier_earned
GROUP BY uid
) t1
ON u.uid = t1.uid
LEFT JOIN tbl_tier t2
ON t1.max_tier_id = t2.tier_id;

Answer 2

SQL Fiddle
MySQL 5.6 Schema Setup:
CREATE TABLE tbl_user
(`uid` int, `first_name` varchar(6), `last_name` varchar(6), `email_id` varchar(18))
;
INSERT INTO tbl_user
(`uid`, `first_name`, `last_name`, `email_id`)
VALUES
(1, 'steve', 'martin', 'steve1#gmail.com'),
(2, 'mark', 'lee', 'mark1#gmail.com'),
(3, 'nelson', 'wise', 'nelson23#gmail.com')
;
CREATE TABLE tbl_tier
(`tier_id` int, `tier_name` varchar(8), `points_required` int)
;
INSERT INTO tbl_tier
(`tier_id`, `tier_name`, `points_required`)
VALUES
(1, 'Silver', 100),
(2, 'Gold', 200),
(3, 'Platinum', 300)
;
CREATE TABLE tbl_tier_earned
(`id` int, `tier_id` int, `uid` int)
;
INSERT INTO tbl_tier_earned
(`id`, `tier_id`, `uid`)
VALUES
(1, 1, 1),
(2, 2, 1),
(3, 3, 1),
(4, 1, 2),
(5, 2, 2),
(6, 1, 3)
;
Query 1:
SELECT c.first_name, c.last_name, c.email_id,
(SELECT tier_name from tbl_tier WHERE points_required = max(b.points_required)) as current_tier
FROM tbl_tier_earned a
INNER JOIN tbl_tier b ON a.tier_id = b.tier_id
INNER JOIN tbl_user c ON a.uid = c.uid
GROUP BY c.first_name, c.last_name, c.email_id
Results:
| first_name | last_name | email_id | current_tier |
|------------|-----------|--------------------|--------------|
| mark | lee | mark1#gmail.com | Gold |
| nelson | wise | nelson23#gmail.com | Silver |
| steve | martin | steve1#gmail.com | Platinum |