Trying to COUNT the same table for different values - mysql

Question

I have a table called flags from which I'm trying to extract two COUNTs.
I'd like one COUNT for the number of flags since the start of the year and a separate COUNT for this week's allocation.
The query I'm using is as follows:
SELECT
COUNT(f1.ID) AS `Total Flags`,
COUNT(f2.ID) AS `Weekly Flags`
FROM `frog_flags`.`flags` f1
LEFT JOIN `frog_flags`.`flags` f2
ON f1.`ID` = f2.`ID`
WHERE
f2.`Datetime` > '2013-07-08 00:00:00'
AND
( f1.`Staff_ID` = '12345' AND f2.`Staff_ID` = '12345')
AND
f1.`Datetime` > '2012-09-01 00:00:00'
Even though I have data in place, it's showing 0 for both the Total Flags and the Weekly Flags.
I suspect I've confused my WHERE clauses for trying to JOIN the same table twice.
Am I using my clauses incorrectly when trying to COUNT the same table for different values?

Answer 1

This is a cross-tab SQL query - it's a great design pattern once you get the hang of it:
SELECT
sum( case when `Datetime`> '2012-09-01 00:00:00' then 1 else 0 end) AS `Total Flags`,
sum( case when `Datetime`> '2013-07-08 00:00:00' then 1 else 0 end) AS `Weekly Flags`
FROM `frog_flags`.`flags` f1
WHERE f1.`Staff_ID` = '12345'
You use a condition to create basically boolean flags which get summed up - this allows for a number of predefined new columns instead of rows.
You could take it further and do it for all staff simultaneously:
SELECT
f1.`Staff_ID`,
sum( case when `Datetime`> '2012-09-01 00:00:00' then 1 else 0 end) AS `Total Flags`,
sum( case when `Datetime`> '2013-07-08 00:00:00' then 1 else 0 end) AS `Weekly Flags`
FROM `frog_flags`.`flags` f1
WHERE f1.`Staff_ID` = '12345'
GROUP BY f1.`Staff_ID`