使用查询（SQL）从所有三个表中获取数据

Question

In my database, I have 3 tables.

Jokes:

CREATE TABLE IF NOT EXISTS `jokes` (
  `joke_id` int(11) NOT NULL AUTO_INCREMENT,
  `joke` varchar(1024) NOT NULL,
  `category_id` int(11) NOT NULL,
  `vote` int(255) NOT NULL,
  `date_added` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`joke_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

Category:

CREATE TABLE IF NOT EXISTS `category` (
  `category_id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(51) NOT NULL,
  PRIMARY KEY (`category_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

And finally, Comments:

CREATE TABLE IF NOT EXISTS `comments` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user` varchar(40) NOT NULL,
  `comment` text NOT NULL,
  `joke_id` int(11) NOT NULL,
  `post_id` int(11) NOT NULL,
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

These three tables need to be joined together to get data from each. So far i have used these three queries with no luck in getting what i need.

what i need this query to do is

• Assign the joke_id to the joke_id in the comments, and also displays the joke_id in the view.
• Assign the category_id of a joke to the name and display it
• grab the votes
• grab the jokes

1st query - this query does actually grab all the data i want, but at the same time does not grab the joke_id and pass it to view (as i need the joke_id to assign comments to that unique id):

SELECT j.*, c.name, 
co.* FROM jokes j LEFT 
JOIN category c ON c.category_id 
= j.category_id LEFT JOIN 
comments co ON co.joke_id = 
j.joke_id WHERE j.joke_id = '$joke_id'

2nd query - This query joins the category to the correct one, and displays the joke and joke_id for me to assign comments to. But it does not show any comments

SELECT j.*, c.name 
FROM jokes j LEFT JOIN category c 
ON c.category_id = j.category_id 
WHERE joke_id = '$joke_id'

3rd query - This query was provided by a user on stack overflow, but seems to throw a tonne of errors my way when a there is no comment attatched to that joke

SELECT c.*, j.*, co.*
FROM jokes j
INNER JOIN category c ON c.category_id = j.category_id
INNER JOIN comments co ON co.joke_id = j.joke_id
WHERE j.joke_id =  '$joke_id'

Any help altering this query to get all the items in the three database together would be much appreciated!

Answer 1

Edit the selected fields to suits your needs. Also if you want to display only one joke and its data you have to set the id of the joke you want as you did on the WHERE for instance.

SELECT jokes.*, category.*, comments.* FROM jokes LEFT JOIN category ON jokes.category_id = category.category_id LEFT JOIN comments ON jokes.jokes_id = comments.joke_id