Question

So basically I’m getting notifications of new content on my website. I have 4 tables –

• articles
• media
• updates
• comments

Each table has a set of its own columns (I can include these if anyone wants). There is one distinct column every table has, this is the timestamp column (a big int formatted column with data from the PHP time() function). My solution to getting the last 30 modifications is to select the first 30 rows from these 4 tables ordered by timestamp descending.

Here is the query I have so far, it doesn’t work and I’m wondering if someone could help me. –

SELECT * FROM `articles` 
UNION SELECT * FROM `media` 
UNION SELECT * FROM `updates` 
UNION SELECT * FROM `comments` 
ORDER BY `timestamp` DESC 
LIMIT 30

EDIT:
I was also using another query before –

SELECT * FROM `articles` ,`media` ,`updates` ,`comments` 
ORDER BY `timestamp` DESC 
LIMIT 30

and kept getting this error –
Column ‘timestamp’ in order clause is ambiguous

EDIT 2

I realise now I have to use the AS clause in my statement to combine these results into one table.

Answer 1

SELECT a.*,m.*,u.*,c.* from articles AS a
LEFT JOIN media AS m ON (m.timestamp = a.timestamp)
LEFT JOIN updates AS u ON (u.timestamp = a.timestamp)
LEFT JOIN comments AS c ON (c.timestamp = a.timestamp)
ORDER BY timestamp desc LIMIT 30