Combining two similar queries together - mysql

Question

I have MySQL queries both of which work fine independantly which I would like to combine together so I get three values returned.
Query 1 checks how many accounts have been deleted:
SELECT
COUNT(1) AS deleted_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date
FROM
exit_reasons e
WHERE
e.timestamp>='$sixmonths'
GROUP BY
WEEKOFYEAR(e.timestamp)
ORDER BY
display_date ASC
LIMIT 26
This returns a date and the number who deleted in that week
Query 2 checks how many of these have subsequently signed up again:
SELECT
COUNT(1) AS date_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date
FROM
exit_reasons e
LEFT JOIN
companies c on e.email=c.email
WHERE
e.timestamp>='$sixmonths' AND c.email IS NOT NULL
GROUP BY
WEEKOFYEAR(e.timestamp)
ORDER BY
display_date ASC
LIMIT 26
This returns a date and the number of that weeks deleted who now have a new account
I would like it to return a date and then the number deleted and number rejoined in one query so I tried:
SELECT
COUNT(1) AS date_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date,
date_count as rejoined_count from
(SELECT
COUNT(1) AS date_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date
FROM
exit_reasons e2
LEFT JOIN
companies c on e.email=c.email
LEFT JOIN
companies_users cu on e.email=cu.email
WHERE
e2.timestamp>='$sixmonths' AND c.email IS NOT NULL
GROUP BY
WEEKOFYEAR(e.timestamp)
ORDER BY
display_date ASC
LIMIT 26)
FROM
exit_reasons e
WHERE
e.timestamp>='$sixmonths'
GROUP BY
WEEKOFYEAR(e.timestamp)
ORDER BY
display_date ASC
LIMIT 26
but I am getting a syntax error - how can I combine these queries together into one query?

Answer 1

You should be able to combine the two queries into a single query by using an aggregate function along with some conditional logic like a CASE expression:
SELECT
COUNT(1) AS deleted_count,
SUM(CASE WHEN c.email IS NOT NULL THEN 1 ELSE 0 END) as date_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date
FROM exit_reasons e
LEFT JOIN companies c
on e.email=c.email
WHERE e.timestamp>='$sixmonths'
GROUP BY WEEKOFYEAR(e.timestamp)
ORDER BY display_date ASC
LIMIT 26;
See Demo. Your check on the second query if the c.email IS NOT NULL is moved into the SUM(CASE.. which allows you to get a total of the rows that are not null.

Answer 2

I think the following will do what you want:
SELECT COUNT(*) AS deleted_count,
COUNT(c.email) as date_count,
SUBDATE(e.timestamp, INTERVAL WEEKDAY(e.timestamp) DAY) AS display_date
FROM exit_reasons e LEFT JOIN
companies c
on e.email = c.email
WHERE e.timestamp >= '$sixmonths'
GROUP BY WEEKOFYEAR(e.timestamp)
ORDER BY display_date ASC
LIMIT 26;
In the event that someone can sign up more than once with the same email, you should change the count() to use distinct:
COUNT(DISTINCT e.email) as deleted_count,
COUNT(DISTINCT c.email) as date_count