postgresql group by - mysql

Question

This is my query in Postgresql:
SELECT
C.id, S.domen, B.name, C.source_id, ST.name
FROM "calls" C
INNER JOIN "site" S ON S.id=C.site_id
INNER JOIN "sources" ON sources.id=C.source_id
INNER JOIN "brand" B ON B.id = S.id_brand
INNER JOIN "source_types" ST ON ST.id = "sources".type_id
WHERE
("calltime" >= '2017-12-01') AND
("calltime" <= '2017-12-03') AND
(S."id_brand"='6')
ORDER BY "calltime" LIMIT 50
And I get this result:
Now I am trying to group by name(last column) this result to get result like this:
Контекстная реклама - 17
SEO-10
....
And for this I use this query:
SELECT
ST.name, count(ST.name)
FROM "calls" C
INNER JOIN "site" S ON S.id=C.site_id
INNER JOIN "sources" ON sources.id=C.source_id
INNER JOIN "brand" B ON B.id = S.id_brand
INNER JOIN "source_types" ST ON ST.id = "sources".type_id
WHERE
("calltime" >= '2017-12-01') AND
("calltime" <= '2017-12-03') AND
(S."id_brand"='6')
GROUP BY ST.name
ORDER BY count(ST.name) DESC LIMIT 50
But I am getting wrong result:
Seems like it take values from source_id column.
what am I doing wrong?

Answer 1

Try this, If you call group by before limit the result then group by for the entire records. So first filter then do the group by.
SELECT
name, count(name)
FROM(
SELECT
ST.name
FROM "calls" C
INNER JOIN "site" S ON S.id=C.site_id
INNER JOIN "sources" ON sources.id=C.source_id
INNER JOIN "brand" B ON B.id = S.id_brand
INNER JOIN "source_types" ST ON ST.id = "sources".type_id
WHERE
("calltime" >= '2017-12-01') AND
("calltime" <= '2017-12-03') AND
(S."id_brand"='6')
ORDER BY "calltime" LIMIT 50
) T
GROUP BY name

Answer 2

The LIMIT 50 in the second query is executed after the GROUP BY.
If you want to aggregate only the first 50 lines, write the LIMIT 50 into a subselect and perform the GROUP BY in the outer SELECT.

Answer 3

It's possible that the 49 is just a coincidence. Try:
SELECT
ST.name, count(*)
FROM "calls" C
INNER JOIN "site" S ON S.id=C.site_id
INNER JOIN "sources" ON sources.id=C.source_id
INNER JOIN "brand" B ON B.id = S.id_brand
INNER JOIN "source_types" ST ON ST.id = "sources".type_id
WHERE
("calltime" >= '2017-12-01') AND
("calltime" <= '2017-12-03') AND
(S."id_brand"='6') AND
C.source_id > 50
GROUP BY ST.name
ORDER BY count(*) DESC LIMIT 50
All I did was change it to count(*) and add AND C.source_id > 50 to the Where clause. Let's see if this changes the count.
Also you could just run this:
SELECT
count(*)
FROM "calls" C
INNER JOIN "site" S ON S.id=C.site_id
INNER JOIN "sources" ON sources.id=C.source_id
INNER JOIN "brand" B ON B.id = S.id_brand
INNER JOIN "source_types" ST ON ST.id = "sources".type_id
WHERE
("calltime" >= '2017-12-01') AND
("calltime" <= '2017-12-03') AND
(S."id_brand"='6')
This gives you a total count of all the rows (I removed the GROUP BY). If this number equals the total of your grouped row counts, then they really are the counts. We are looking for 127 which is 49 + 30 + 21 + 13 + 9 + 4 + 1
I hope this helps.