How do I count distinct rows with duplicates in a table?

Question

I have a problem with my homework and maybe somebody could help me:

I need a select query to have as a result two columns: one named 'Date' with distinct rows (no duplicates) from the column ab_datum and one column called 'Number', that counts the rows from ab_datum.

I've tried this:

>select distinct ab_datum Date, count(distinct ab_datum) Number
from abflug
order by ab_datum;

But of course it didn't work - I've tried some other solutions, but I didn't help.

This is the table I have to work with:

AB_DATUM	F_BEZ	HERST	TYP	PER_NR	SER_NR	AB_ZEIT
06.07.13	LH-888	Boeing	B747	9fg-he-ztu8	10010071	11.23
08.10.13	LH-238	Airbus	A320	z3et-bwe7	10010072	22.06
13.11.13	LH-341	Boeing	B737	ba23-0012	10010001	10.23
14.11.13	LH-358	Boeing	B737	ba23-0012	10010001	8.17
13.11.13	LH-553	Boeing	B777	xv23-0889	10010002	16.53
15.11.13	LH-421	Boeing	B777	xv56-3142	10010002	14.45
17.11.13	LH-789	Airbus	A330	45-6789	10010003	8.11
14.11.13	LH-112	Boeing	B737	ba23-0034	10010001	8.14
17.11.13	LH-421	Boeing	B777	xv23-0889	10010002	16.26
18.11.13	LH-223	Airbus	A380	ab-45-6xf	10010004	9.45
19.11.13	LH-634	Airbus	A350	5478-awe3	10010005	20.25
18.02.14	LH-238	Airbus	A320	z3et-bwe7	10010072	23.06

I would be very grateful for your help - I am total beginner in SQL... Thanks!

Answer 1

If you want to count the rows for each date then you need to aggregate with a group by clause:

select ab_datum as "Date", count(*) as "Number"
from abflug
group by ab_datum
order by ab_datum;

Or if the dates have non-midnight times then then truncate those to midnight:

select trunc(ab_datum) as "Date", count(*) as "Number"
from abflug
group by trunc(ab_datum)
order by trunc(ab_datum);

Both date and number are reserved words, so if you really want those as the column aliases then they have to be quoted identifiers .

Answer 2

The first thing that comes to my mind is something like this:

SELECT ab_datum AS "Date", COUNT(*) AS "Number"
FROM abflug
GROUP BY ab_datum
ORDER BY BY ab_datum;

I dont know if this is what you were looking for. If not, please provide more information about your desired result.