Postgresql Use count on multiple columns - postgresql

Question

I have two tables. The first generate the condition for counting records in the second. The two tables are linked by a relation of 1:1 by Timestamp.
The problem is that the second table have many columns, and we need a count for each column that match the condition in the first column.
Example:
Tables met and pot
CREATE TABLE met (
tstamp timestamp without time zone NOT NULL,
h1_rad double precision,
CONSTRAINT met_pkey PRIMARY KEY (tstamp)
)
CREATE TABLE pot (
tstamp timestamp without time zone NOT NULL,
c1 double precision,
c2 double precision,
c3 double precision,
CONSTRAINT met_pkey PRIMARY KEY (tstamp)
)
REALLY pot have 108 columns from c1 to c108.
Tables values:
+ Table met + + Table pot +
+----------------+--------+--+----------------+------+------+------+
| tstamp | h1_rad | | tstamp | c1 | c2 | c3 |
+----------------+--------+--+----------------+------+------+------+
| 20150101 00:00 | 0 | | 20150101 00:00 | 5,5 | 3,3 | 15,6 |
| 20150101 00:05 | 1,8 | | 20150101 00:05 | 12,8 | 15,8 | 1,5 |
| 20150101 00:10 | 15,4 | | 20150101 00:10 | 25,4 | 4,5 | 1,4 |
| 20150101 00:15 | 28,4 | | 20150101 00:15 | 18,3 | 63,5 | 12,5 |
| 20150101 00:20 | 29,4 | | 20150101 00:20 | 24,5 | 78 | 17,5 |
| 20150101 00:25 | 13,5 | | 20150101 00:25 | 12,8 | 5,4 | 18,4 |
| 20150102 00:00 | 19,5 | | 20150102 00:00 | 11,1 | 25,6 | 6,5 |
| 20150102 00:05 | 2,5 | | 20150102 00:05 | 36,5 | 21,4 | 45,2 |
| 20150102 00:10 | 18,4 | | 20150102 00:10 | 1,4 | 35,5 | 63,5 |
| 20150102 00:15 | 20,4 | | 20150102 00:15 | 18,4 | 23,4 | 8,4 |
| 20150102 00:20 | 6,8 | | 20150102 00:20 | 16,8 | 12,5 | 18,4 |
| 20150102 00:25 | 17,4 | | 20150102 00:25 | 25,8 | 23,5 | 9,5 |
+----------------+--------+--+----------------+------+------+------+
What i need is the number of rows of pot where value is higher than 15 when in met the value is higher than 15 with the same timestamp, grouped by day.
With the data supplied we need something like:
+----------+----+----+----+
| day | c1 | c2 | c3 |
+----------+----+----+----+
| 20150101 | 3 | 2 | 1 |
| 20150102 | 2 | 4 | 1 |
+----------+----+----+----+
How can i get this ?
Is this possible with a single query even with subquerys ?
Actually the raw data is stored every minute in others tables. The tables met and pot are summarized and filtered tables for performance.
If necessary, i can create tables with data summarized by days if this simplify the solution.
Thanks
P.D.
Sorry for my english

Answer 1

You can solve this with some CASE statements. Test for both conditions, and if true return a 1. Then SUM() the results using a GROUP BY on the timestamp converted to a date to get your total:
SELECT
date(met.tstamp),
SUM(CASE WHEN met.h1_rad > 15 AND pot.c1 > 15 THEN 1 END) as C1,
SUM(CASE WHEN met.h1_rad > 15 AND pot.c2 > 15 THEN 1 END) as C2,
SUM(CASE WHEN met.h1_rad > 15 AND pot.c3 > 15 THEN 1 END) as C3
FROM
met INNER JOIN pot ON met.tstamp = pot.tstamp
GROUP BY date(met.tstamp)