如何从两个不同的表中进行选择和计数，以在一个查询中获得帖子的“喜欢计数”？

Question

I'm kind of noobie to this, but I'm trying to learn, I have two tables, the first one (NEWS) has all the information about posts of a blog, it has the follow structure:

* NEWS (TABLE 1)
- id_new
- id_category
- date
- ...etc
- **likes**

and I have a second table:

* LIKES (TABLE 2)
- id_like
- id_new
- id_user
- date
- ip_user

So, I want to select all the rows from TABLE 1 to display all the news but also i want to count the likes and get the COUNT of each new as like column.

Answer 1

You can do it like this

SELECT table1.*, table2.*, count(table2.id_like) as like FROM news AS table1 
INNER JOIN likes AS table 2 ON table1.id_new = table2.id_new;

OR

SELECT table1.*, table2.*, count(table2.id_like) as like FROM news AS table1 
LEFT JOIN likes AS table 2 ON table1.id_new = table2.id_new;

Answer 2

you can use prepared statement

for example

$stmt = $pdo->prepare("SELECT count(*) FROM TABLE_1 );

$stmt2 = $pdo->prepare("SELECT count(*) FROM TABLE_2 );

//then execute

just read more on prepared statement

Answer 3

尝试这个

SELECT n, (SELECT count(*) FROM like l WHERE l.id_new = n.id_new) FROM news n

Answer 4

使用类似：

SELECT *, (SELECT COUNT(*) FROM LIKES WHERE LIKES.id_new =id_new) AS newsLikesCount FROM NEWS ORDER BY date;

Answer 5

This approach left joins the NEWS table to a subquery which finds the number of likes for each news story.

SELECT
    t1.*,
    COALESCE(t2.likes, 0) AS likes
FROM NEWS t1
LEFT JOIN
(
    SELECT id_new, COUNT(*) AS likes
    FROM LIKES
    GROUP BY id_new
) t2
    ON t1.id_new = t2.id_new

Note that here a story having no likes would not appear at all in the LIKES table and would receive a count of zero. Also note that I assume that every record in the LIKES table corresponds to a logical like. If not, then the query could be modified to count something else.

Answer 6

This query would return all news and their number of likes

select n1.* , numberOfLikes.number_of_likes
from news n1 
left join 
(select n.id_news, count(l.id_like) as number_of_likes
from news n 
left join likes l on n.id_news = l.id_new
group by n.id_news) numberOfLikes on n1.id_news = numberOfLikes.id_news

The important concepts here is understanding how two tables are joined together (1), how group by works(2), and how to aggregate l.id_likes using count (3).

(1). Left join preserves everything in the NEWS table and join them with news link to the news.

(2). Then we group the rows base on id_news from the news. However, mysql gets confused because it doesn't know what to do with id_like from the likes table that we included in our select clause. Don't worry my friend, This is where count comes in.

(3). We count the number of id_likes base for each id_news since we are grouping the rows base on id_news.

I hope this helps. and welcome to StackOverfow. If you find this answer of any other answer helpful please mark it as the solution. That way it will help the community and fellow programmers in the future if they run into the same problem as you. Cheers.

Edit: to include all columns from news table we simply join the result from above back to the news table itself. and we select everything from the news table n1 and only number_of_likes from the result we created above.