MySQL查询帮助获取结合两个表的数据

Question

I have following tables

articles_category

id    title    sef_title

articles_data

id    cat_id    title    sef_title    details

On each table "id" is the primary key and articles_data.cat_id is foreign key of articles_category

I need to fetch one latest article data for each articles category with following data.

articles_category.id
articles_category.title
articles_category.sef_title
articles_data.id
articles_data.cat_id
articles_data.title
articles_data.sef_title
articles_data.details

I tried with following query but it displays first article (oldest entry) rather than latest one.

SELECT
    articles_category.id as article_cat_id, articles_category.sef_title as cat_sef_title, articles_category.title as cat_title,
    articles_data.id, articles_data.cat_id as listing_cat_id, articles_data.title, articles_data.sef_title, articles_data.details
FROM articles_category, articles_data
WHERE articles_category.id = articles_data.cat_id
GROUP BY articles_data.cat_id
ORDER BY articles_data.id DESC

Answer 1

if it's a one to many relation, try (untested):

SELECT * 
FROM articles_category, articles_data 
WHERE articles_category.id = articles_data.cat_id 
  AND articles_data.id in (
     SELECT max(articles_data.id) 
     FROM articles_data GROUP BY cat_id
  )

you are not guaranteed a particular row on a GROUP BY

and you should really use a date on your article as the max id is never guaranteed to be the latest article even if you are using autoincrement

Answer 2

ORDER affects the display of records after the GROUP function has been performed. The GROUP function recognizes the first record it sees in its search.

What you need to do is perform 2 queries. The first one should be

SELECT max(articles_data.id), articles_data.cat_id ... 
GROUP BY articles_data.cat_id

The second query should fetch the associated records using those resultant primary keys.

Answer 3

A possibility is to create another value such as date_created and place a time stamp there when creating an entry.

Then you would just have to ORDER BY date.