mysql combine 2 table with a common group by column - mysql

Question

i've 2 tables with date, in timestamp format,
i have to count how many record there are every week in total...
...and have the result in just one query...
so i'll explain it better with examples:
2 table, the first one:
table name: visitor
ID | time | ref (now i put in fake timestamp in time column sorry)
--------------------
1 | 3455 | john
2 | 3566 | ted (week 40)
3 | 8353 | ted (week 38)
4 | 6673 | katy
5 | 6365 | ted (week 40)
6 | 4444 | john
7 | 3555 | ted (week 40)
and the second one (very similar):
table name: users
ID | time | ref (now i put in fake timestamp in time column sorry)
--------------------
1 | 3455 | ted (week 41)
2 | 3566 | ted (week 42)
3 | 8353 | ted (week 40)
4 | 6673 | katy
5 | 6365 | ted (week 41)
6 | 4444 | john
7 | 3555 | ted (week 38)
8 | 6789 | ted (week 43)
i do this query and i obtain this result:
SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS tot
FROM visitor WHERE ref='ted' GROUP BY week
table result #1
week | tot
----------
38 | 1
40 | 3
43 | 1
the i do the some for the second table:
SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS totuser
FROM users WHERE ref='ted' GROUP BY week
table result #2
week | totuser
----------
38 | 1
40 | 1
41 | 2
42 | 1
but i want with just one query do this result:
week | tot | totusers
---------------------- (when both are 0 doent appear -like 39 for example-)
38 | 1 | 1
40 | 3 | 1
41 | 0 | 2
42 | 0 | 1
43 | 1 | 0
i know that i've to use LEFT JOIN, GROUP BY and IFNULL but i'm doing always something wrong and i cant figure it out.
order by WEEK desc
thank u for any help.

Answer 1

Technically, what you want is a full outer join, but MySQL does not support that. I approach this using union all and group by:
SELECT weeek, SUM(visitors) as visitors, SUM(users) as users
FROM ((SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS visitors, 0 as users
FROM visitor
WHERE ref='ted'
GROUP BY week
) UNION ALL
(SELECT WEEK(FROM_UNIXTIME(time)) AS week, 0, COUNT( * )
FROM users
WHERE ref ='ted'
GROUP BY week
)
) w
GROUP BY week
ORDER BY week;
Note: As in your data, this will only include weeks that have either visitors or users. If you want weeks with neither, it is best to start with a table containing all the weeks you want (some sort of calendar table).