Select Missing Date Ranges In table In Oracle - sql

Question

I have the following Data Table Data as:
EMPLOYEEID DAYDATE
-----------------------------------
101 01/08/2017
101 02/08/2017
101 04/08/2017
101 06/08/2017
101 07/08/2017
102 01/08/2017
102 03/08/2017
102 06/08/2017
I want to Write a Query to get the following missing Dates between
01/8/2017 to
07/08/2017 Data as :
EMPLOYEEID DAYDATE
-----------------------------------
101 03/08/2017
101 05/08/2017
101 07/08/2017
102 02/08/2017
102 04/08/2017
102 05/08/2017
102 07/08/2017
How to deal with That?!

Answer 1

Either use a Date table, which I think is better, or use a Derived table to populate the dates(many codes available in google under "Oracle How to generate dates") :
SELECT t.employeeid,s.date
FROM (SELECT distinct p.employeeid FROM YourTable p) t
CROSS JOIN ( DATE TABLE \ Derived Table) s
This query will generate the entire range of dates for each employee. If you want only those that are missing:
SELECT t.employeeid,s.date
FROM (SELECT distinct p.employeeid FROM YourTable p) t
CROSS JOIN ( DATE TABLE \ Derived Table) s
LEFT JOIN YourTable h
ON(h.employeeID = t.employeeId and h.date = s.date)
WHERE h.employeeID IS NULL

Answer 2

You can generate all the rows with a hierarchical query:
SELECT DATE '2017-08-01' + LEVEL - 1 AS dt
FROM DUAL
CONNECT BY DATE '2017-08-01' + LEVEL - 1 <= DATE '2017-08-07'
or a recursive sub-query factoring clause:
WITH alldates ( dt ) AS (
SELECT DATE '2017-08-01' FROM DUAL
UNION ALL
SELECT dt + 1 FROM alldates WHERE dt < DATE '2017-08-07'
)
SELECT * FROM alldates
Then you can use a partitioned outer join combine it with your existing data nad filter for those missing rows:
WITH alldates ( dt ) AS (
SELECT DATE '2017-08-01' FROM DUAL
UNION ALL
SELECT dt + 1 FROM alldates WHERE dt < DATE '2017-08-07'
)
SELECT employeeId,
dt
FROM alldates d
LEFT OUTER JOIN
your_table t
PARTITION BY ( t.employeeID )
ON ( t.daydate = d.dt )
WHERE daydate IS NULL;

Answer 3

Assuming you have a table EMPLOYEE in which EMPLOYEEID is primary key - and assuming that there may be employees who don't appear in your DATA_TABLE at all, and they must be then included in your output:
select e.employeeid, d.daydate
from employee e cross join ( select date '2017-08-01' + level - 1 as daydate
from dual
connect by level <= 7
) d
where (e.employeeid, d.daydate) not in (select employeeid, daydate from data_table)
;