2表上的MySQL内部联接不起作用

Question

I have a table in my database named contacts and a table named views.

On the table contacts I have the following fields:

• id
• status
• first_name
• last_name

The status can be cold, prospect or lost.

On the table views I have the following fields:

• user_id
• art_views
• art_title

The relation between those 2 tables is id and user_id.

I need a query to make a new html table with the following columns:

• art_title
• cold
• prospect
• lost

Now I have the following query (UPDATED):

SELECT
v.art_title,
SUM(CASE c.status WHEN 'cold' THEN v.art_views ELSE 0 END) cold,
SUM(CASE c.status WHEN 'prospect' THEN v.art_views ELSE 0 END) prospect,
SUM(CASE c.status WHEN 'lost' THEN v.art_views ELSE 0 END) lost
FROM views v
JOIN contacts c ON v.user_id = c.id
GROUP BY v.art_title

This query is working now (thanks to Gerv) but i still have users who don't have a status. So i leave the field user_id in the table 'views' empty. How can i change the query for those users so i can count them also?

I tried to: SUM(CASE v.user_id WHEN ' ' THEN v.art_views ELSE 0 END) test, but with no result here.

Answer 1

You can switch the logic by selecting from the views table and joining de contacts table. Below query will pivot the status with a CASE clause

SELECT
    v.art_title,
    SUM(CASE c.status WHEN 'cold' THEN v.art_views ELSE 0 END) cold,
    SUM(CASE c.status WHEN 'prospect' THEN v.art_views ELSE 0 END) prospect,
    SUM(CASE c.status WHEN 'lost' THEN v.art_views ELSE 0 END) lost,
    SUM(CASE c.status WHEN NULL THEN v.art_views ELSE 0 END) no_user
FROM views v
LEFT JOIN contacts c ON v.user_id = c.id
GROUP BY v.art_title
ORDER BY (cold+lost+prospect+no_user) DESC
LIMIT 10

Answer 2

尝试

SELECT art_title, SUM(art_views), status FROM contacts AS c INNER JOIN views AS v ON v.user_id = c.id GROUP BY v.art_title, c.status