Mysql group joins same id together but still get duplicates [duplicate] - mysql

Question

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Selecting from two tables with inner join and limit [duplicate]
(5 answers)
Closed last year.
I would like to group posts with same id. Now i get duplicate of posts based on how many comments. Which is wrong, it should group and show the latest comment and not create row for each comment
Table structure:
CREATE TABLE users(
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(255),
myKey VARCHAR(100)
);
INSERT INTO users (name, myKey)
VALUES ("Gregor", "kx4ht"),
("Liza", "1lPxk"),
("Matt", "mP3fd"),
("Bob", "zStr5");
CREATE TABLE comments(
id INT PRIMARY KEY AUTO_INCREMENT,
post_id INT,
comment VARCHAR(255)
);
INSERT INTO comments (post_id, comment)
VALUES (1, "Hello world"),
(2, "I like iceCream"),
(1, "I like unicorns");
CREATE TABLE post(
id INT PRIMARY KEY AUTO_INCREMENT,
user_id INT,
text VARCHAR(255),
last_comment INT,
FOREIGN KEY (`last_comment`) REFERENCES `comments` (`id`)
);
INSERT INTO post (user_id, text, last_comment)
VALUES (1, "My first post", 3),
(1, "What is this?", 2);
Query:
SELECT u.name, p.text, c.comment
FROM post p
INNER JOIN users u ON (u.id = p.user_id)
INNER JOIN comments c ON (c.post_id = p.id)
WHERE (p.user_id = 1)
GROUP BY p.id, c.id;
Now
name text comment
Gregor My first post Hello world
Gregor What is this? I like iceCream
Gregor My first post I like unicorns
What i expect:
name text comment
Gregor What is this? I like iceCream
Gregor My first post I like unicorns

Answer 1

This should solve your issue
SELECT u.name, p.text, c.comment
FROM post p
INNER JOIN users u ON (u.id = p.user_id)
INNER JOIN
(
SELECT *
FROM comments c1
WHERE NOT EXISTS (
SELECT *
FROM comments c2
WHERE c1.post_id = c2.post_id AND
c1.id < c2.id
)
) c ON (c.post_id = p.id)
WHERE (p.user_id = 1)
GROUP BY p.id, c.id;