Counting distinct dates from two columns in a single SQL table - mysql

Question

I've been reading through the solutions of similar problems posted here, but none seem to resolve my particular issue.
I currently have a table (CT_JOINED) that includes three columns: an identifer column (TUMOURID), a date column (AVCT_DATE) and another date column (OPDATE).
As an example, the columns for two IDs look as follows:
ID, AVCT_DATE, OPDATE
1, 06-APR-13, 06-APR-13
1, 06-APR-13, 14-JUN-13
1, 06-APR-13, 22-JUN-13
2, 03-APR-14, 10-DEC-15
2, 03-APR-14, 31-DEC-15
What I'm attempting to do is create a column that is equal to the number of unique dates per ID. So the result for ID 1 would be 3 and the result for ID 2 would be 3.
I have attempted a count of distinct values across the two columns, but this does not provide the answers above (it instead reports values of 3 and 2 respectively):
select TUMOURID, COUNT(DISTINCT(AVCT_DATE || OPDATE)) AS COUNT
FROM CT_JOINED
GROUP BY TUMOURID;
The same thing happens if I try and do the same in a new table:
CREATE TABLE CT_DISTINCT AS (
SELECT TUMOURID, COUNT(*) AS COUNT
FROM (
SELECT DISTINCT TUMOURID, AVCT_DATE, OPDATE
FROM CT_JOINED)
GROUP BY TUMOURID
);
I'm at a loss. Is it possible?

Answer 1

You could use:
SELECT TUMOURID, COUNT(DISTINCT d) AS cnt
FROM (select TUMOURID, AVCT_DATE AS d
FROM CT_JOINED
UNION ALL
SELECT TUMOURID, OPDATE AS d) sub
GROUP BY TUMOURID;

Answer 2

Unpivot the data and then use count(distinct) or remove duplicates along the way:
select tumourid, count(*)
from ((select tumourid, avct_date as dte
from ct_joined
) union -- intentional to remove duplicates
(select tumourid, opdate as dte
from ct_joined
)
) t
group by tumourid;

Answer 3

Use UNION to avoid duplicate date & just use count(*) :
SELECT tumourid, COUNT(date)
FROM ((SELECT tumourid, avct_date AS date
FROM ct_joined
) UNION
(SELECT tumourid, opdate
FROM ct_joined
)
) t
GROUP BY tumourid;

Answer 4

All of the answers below work like a charm with a few tweaks to also account for rows with null values. For instance:
SELECT TUMOURID, COUNT(*)
FROM ((SELECT TUMOURID, AVCT_DATE AS DTE
FROM CT_JOINED
WHERE AVCT_DATE IS NOT NULL
) UNION
(SELECT TUMOURID, OPDATE AS DTE
FROM CT_JOINED
WHERE OPDATE IS NOT NULL
)
) T
GROUP BY TUMOURID;
Many thanks.