Returning Only Latest Result For Location in SQL [duplicate] - sql

Question

This question already has answers here:
How do I limit the number of rows returned by an Oracle query after ordering?
(14 answers)
Closed last year.
I'm wanting to find the very last pallet placed in a given batch of locations within a warehouse.
I currently have:
SELECT
max(datreg) AS "_Reg Date",
logguser,
mha,
rack,
horcoor,
vercoor
FROM
L16T3
WHERE
l16lcode = '3'
AND
rack = #('Rack?',rack)
AND
horcoor >= #('Loc From?',horcoor)
AND
horcoor <= #('Loc To?',horcoor)
ORDER BY 1
LIMIT 1
I thought this would return just the last pallet placed in that specific location, but I'm still getting like 4 entries for one location.
I would only want the highlighted result, as that is the most recent pallet placed in 110-001-04:
I'm sure this is super simple but im just starting out :)

Answer 1

You can use a combination of ORDER BY and LIMIT to achieve what you want.
Limit
In a lot of other databases, this is called LIMIT, but I missed that you are using an Oracle database, which has a different dialect of SQL. In Oracle, the most direct equivilent of a limit is:
FETCH FIRST n ROWS ONLY
This means that your query can return at most n rows. So, for example, FETCH FIRST 1 ROWS ONLY means that it can return at most 1 row. The issue is that it takes rows from the start of the table, not the end (and despite the wording implying FETCH LAST n ROWS ONLY would be a thing, it doesn't seem to be) --- you can essentially think of it as cutting off the rows below given limit.
For example, if I have rows in order "A", "B", and "C", FETCH FIRST 1 ROWS ONLY only returns "A". If "C" was really the one I wanted (e.g. the row at the bottom), then I would need to add an ORDER BY clause to first order the results so that the one I want is at the top.
Order By
ORDER BY column dir orders your results by a specific column in a specific direction, e.g. in ascending (ASC) or descending (DESC) order. The syntax actually allows for more complex ordering (e.g. ordering by multiple columns or by a function), but for this simple case this should do what we need.
Putting it together
You want to order so that your desired row is at the top of your table, then you want to limit your results set to contain at most one row.
Adding something like this to the end of your query should work:
ORDER BY "_Reg Date" DESC
FETCH FIRST 1 ROWS ONLY