Combining date and time fields in ETL SQL Query - sql

Question

I have multiple date and time fields that I need to combine into a datetime in a SQL Query. I unfortunately cannot change the initial database structure to combine them in the original server.
I can combine the SQL Query data after export, but because of the problem of flat files conversion, and the possibility of data corruption/loss, I am hesitant as I would need to convert the flat file twice.
These are the things I've tried:
SELECT Combine = cast([DateValue] as datetime) + Cast([TimeValue] as datetime)
Unfortunately, this leads to errors where I have fewer columns than original fields....
The original Query looks like this:
SELECT
Ordered_Date.DateValue,
Ordered_TOD.TimeValue,
Start_Date.DateValue,
Start_TOD.TimeValue,
End_Date.DateValue,
End_TOD.TimeValue,
Discontinued_Date.DateValue,
Discontinued_TOD.TimeValue
FROM
warehouse_report...........
WHERE
( ..... )
If I add The Combine command into the SQL query, it seems to working in that it is combining the date/time. The issue is that when I implement this in the SELECT section of the SQL Query, I have 1 less column and it won't let me execute the script...
SELECT
Ordered_Date.DateValue,
Ordered_TOD.TimeValue,
Start_Date.DateValue,
Start_TOD.TimeValue,
COMBINE = CAST(End_Date.DateValue as datetime) + CAST(End_TOD.TimeValue as datetime),
Discontinued_Date.DateValue,
Discontinued_TOD.TimeValue
FROM
warehouse_report...........
WHERE
( ..... )
This gives me one less column on the output of the SQL Query...

Answer 1

How about concatenate the values and parse:
SELECT cast([DateValue]||' '||[TimeValue] as datetime)
Please, provide the information about which SGBD you are using to get a better answer.
Edit1:
To SQL Server:
Select
x.d1
From (
Select
convert(datetime, '2018-01-01 00:00:00.0', 121) d1
) x
Union All
Select
convert(datetime,
substring(convert(varchar, x.d1, 121), 1, 11)
+ substring(convert(varchar, x.t1, 121), 11, 13)
, 121)
From (
Select
convert(datetime, '2018-01-01 00:00:00.0', 121) d1,
convert(datetime, '10:00:22') t1
) x