How to combine these queries that group by the same field? - mysql

Question

I have the following three queries
SELECT COUNT(*) as cached_type_a, DATE(datetime) as datetime
FROM requests
WHERE cached = 'a'
GROUP BY DAY(datetime);
SELECT COUNT(*) as cached_type_b, DATE(datetime) as datetime
FROM requests
WHERE cached = 'b'
GROUP BY DAY(datetime);
SELECT COUNT(*) as cached_type_c, DATE(datetime) as datetime
FROM requests
WHERE cached = 'c'
GROUP BY DAY(datetime);
Is it possible to combine them into a single query with 4 columns
cached_type_a, cached_type_b, cached_type_c, datetime?

Answer 1

If you have only three possible values of cache, you can use this,
SELECT DATE(datetime) as datetime,
SUM(CASE WHEN cached = 'a' THEN 1 ELSE 0 END) cached_a,
SUM(CASE WHEN cached = 'b' THEN 1 ELSE 0 END) cached_b,
SUM(CASE WHEN cached = 'c' THEN 1 ELSE 0 END) cached_c
FROM requests
GROUP BY DAY(datetime)
otherwise, if you have multiple number of cache, you can use Prepared Statement
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'SUM(CASE WHEN cached = ''',
cached,
''' then 1 ELSE 0 end) AS ',
CONCAT('cached_',cached)
)
) INTO #sql
FROM requests;
SET #sql = CONCAT('SELECT DATE(datetime) as datetime, ', #sql, '
FROM requests
GROUP BY DAY(datetime)');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Answer 2

SELECT COUNT(a.datetime) as cached_type_a,
COUNT(b.datetime) as cached_type_b,
COUNT(c.datetime) as cached_type_c,
DATE(a.datetime) as datetime
FROM requests a,
requests b,
requests c,
WHERE a.cached = 'a'
and b.cached = 'b'
and c.cached = 'c'
GROUP BY DAY(a.datetime), DAY(b.datetime), DAY(c.datetime);