i am trying to create a view from a SQL table
following is a (very simplified...) subset of data in the table:
in the view i have to show only the EC_MODEL that have Installation as last EC_TYPE
that is, from the table, only the sensor from Station1 should be selected; on the contrary, the EC_MODEL from Station2 must not be selected, because the last operation is a Removal.
Well, I couldn't write the query that does the operation...how could I solve ?
thanks
Try this query:
select
ec_model
from (
select
ec_model, ec_type, rn = row_number() over (partition by ec_model order by operation_date desc)
from
myTable
) t
where
rn = 1
and ec_type = 'installation'
Related
Hi I have a query which looks like the following :
SELECT device_id, tag_id, at, _deleted, data,
row_number() OVER (PARTITION BY device_id ORDER BY at DESC) AS row_num
FROM mdb_history.devices_tags_mapping_history
WHERE at <= '2019-04-01'
AND _deleted = False
AND (tag_id = '275674' or tag_id = '275673')
AND row_num = 1
However when I run the following query, I get the following error :
ERROR: column "row_num" does not exist
Is there any way to go about this. One way I tried was to use it in the following way:
SELECT * from (SELECT device_id, tag_id, at, _deleted, data,
row_number() OVER (PARTITION BY device_id ORDER BY at DESC) AS row_num
FROM mdb_history.devices_tags_mapping_history
WHERE at <= '2019-04-01'
AND _deleted = False
AND (tag_id = '275674' or tag_id = '275673')) tag_deleted
WHERE tag_deleted.row_num = 1
But this becomes way too complicated as I do it with other queries as I have number of join and I have to select the column as stated from so it causes alot of select statement. Any smart way of doing that in a more simpler way. Thanks
You can't refer to the row_num alias which you defined in the same level of the select in your query. So, your main option here would be to subquery, where row_num would be available. But, Postgres actually has an option to get what you want in another way. You could use DISTINCT ON here:
SELECT DISTINCT ON (device_id), device_id, tag_id, at, _deleted, data
FROM mdb_history.devices_tags_mapping_history
WHERE
at <= '2019-04-01' AND
_deleted = false AND
tag_id IN ('275674', '275673')
ORDER BY
device_id,
at DESC;
Too long/ formatted for a comment. There is a reason behind #TimBiegeleisen statement "alias which you defined in the same level of the select". That reason is that all SQL statement follow the same sequence for evaluation. Unfortunately that sequence does NOT follow the sequence of clauses within the statement presentation. that sequence is in order:
from
where
group by
having
select
limits
You will notice that what actually gets selected fall well after evaluation of the where clause. Since your alias is defined within the select phase it does not exist during the where phase.
I'm trying to make a query for acum the sum of one of fields in a new column, but i dont get it in SqlServer 2008 r2
I have the next table:
Fields: id,Codigo,tipo,cantidad
I want to make a query for get the next result
When the field tipo is 2, the acum begins
Is it possible?
Thanks.
finally i found a good sentence for me
with AcumulaCant as (
select
d.idrecno,
d.tipmov,
d.codart,
d.codalm,
d.cant
from movsto d
)
select *,
CantAcum = (
select SUM(cant)
from AcumulaCant c
where c.idrecno <= AcumulaCant.idrecno
and c.codart = AcumulaCant.codart
and c.codalm = AcumulaCant.codalm),
ROW_NUMBER() over(partition by codart,codalm order by idrecno desc) as rn
from AcumulaCant
order by AcumulaCant.codart,AcumulaCant.codalm,AcumulaCant.idrecno desc
With this sentence i get the acum of the sum quantities by ref.
Thanks to all for your comments.
I'm trying to update a column (pop_1_rank) in a postgresql table with the results from a rank() like so:
UPDATE database_final_form_merge
SET
pop_1_rank = r.rnk
FROM (
SELECT pop_1, RANK() OVER ( ORDER BY pop_1 DESC) FROM database_final_form_merge WHERE territory_name != 'north' AS rnk)r
The SELECT query by itself works fine, but I just can't get it to update correctly. What am I doing wrong here?
I rather use the CTE notation.
WITH cte as (
SELECT pop_1,
RANK() OVER ( ORDER BY pop_1 DESC) AS rnk
FROM database_final_form_merge
WHERE territory_name <> 'north'
)
UPDATE database_final_form_merge
SET pop_1_rank = cte.rnk
FROM cte
WHERE database_final_form_merge.pop_1 = cte.pop_1
As far as I know, Postgres updates tables not subqueries. So, you can join back to the table:
UPDATE database_final_form_merge
SET pop_1_rank = r.rnk
FROM (SELECT pop_1, RANK() OVER ( ORDER BY pop_1 DESC) as rnk
FROM database_final_form_merge
WHERE territory_name <> 'north'
) r
WHERE database_final_form_merge.pop_1 = r.pop_1;
In addition:
The column alias goes by the column name.
This assumes that pop_1 is the id connecting the two tables.
You're missing WHERE on UPDATE query, because when doing UPDATE ... FROM you're basically doing joins.
So you need to select primary key and then match on primary key to update just the columns are computing rank over.
So far I have come up with the below:
WHERE (extract(month FROM orders)) =
(SELECT min(extract(month from orderdate))
FROM orders)
However, that will consequently return zero to many rows, and in my case, many, because many orders exist within that same earliest (minimum) month, i.e. 4th February, 9th February, 15th Feb, ...
I know that a WHERE clause can contain multiple columns, so why wouldn't the below work?
WHERE (extract(day FROM orderdate)), (extract(month FROM orderdate)) =
(SELECT min(extract(day from orderdate)), min(extract(month FROM orderdate))
FROM orders)
I simply get: SQL Error: ORA-00920: invalid relational operator
Any help would be great, thank you!
Sample data:
02-Feb-2012
14-Feb-2012
22-Dec-2012
09-Feb-2013
18-Jul-2013
01-Jan-2014
Output:
02-Feb-2012
14-Feb-2012
Desired output:
02-Feb-2012
I recreated your table and found out you just messed up the brackets a bit. The following works for me:
where
(extract(day from OrderDate),extract(month from OrderDate))
=
(select
min(extract(day from OrderDate)),
min(extract(month from OrderDate))
from orders
)
Use something like this:
with cte1 as (
select
extract(month from OrderDate) date_month,
extract(day from OrderDate) date_day,
OrderNo
from tablename
), cte2 as (
select min(date_month) min_date_month, min(date_day) min_date_day
from cte1
)
select cte1.*
from cte1
where (date_month, date_day) = (select min_date_month, min_date_day from cte2)
A common table expression enables you to restructure your data and then use this data to do your select. The first cte-block (cte1) selects the month and the day for each of your table rows. Cte2 then selects min(month) and min(date). The last select then combines both ctes to select all rows from cte1 that have the desired month and day.
There is probably a shorter solution to that, however I like common table expressions as they are almost all the time better to understand than the "optimal, shortest" query.
If that is really what you want, as bizarre as it seems, then as a different approach you could forget the extracts and the subquery against the table to get the minimums, and use an analytic approach instead:
select orderdate
from (
select o.*,
row_number() over (order by to_char(orderdate, 'MMDD')) as rn
from orders o
)
where rn = 1;
ORDERDATE
---------
01-JAN-14
The row_number() effectively adds a pseudo-column to every row in your original table, based on the month and day in the order date. The rn values are unique, so there will be one row marked as 1, which will be from the earliest day in the earliest month. If you have multiple orders with the same day/month, say 01-Jan-2013 and 01-Jan-2014, then you'll still only get exactly one with rn = 1, but which is picked is indeterminate. You'd need to add further order by conditions to make it deterministic, but I have no idea what you might want.
That is done in the inner query; the outer query then filters so that only the records marked with rn = 1 is returned; so you get exactly one row back from the overall query.
This also avoids the situation where the earliest day number is not in the earliest month number - say if you only had 01-Jan-2014 and 02-Feb-2014; comparing the day and month separately would look for 01-Feb-2014, which doesn't exist.
SQL Fiddle (with Thomas Tschernich's anwer thrown in too, giving the same result for this data).
To join the result against your invoice table, you don't need to join to the orders table again - especially not with a cross join, which is skewing your results. You can do the join (at least) two ways:
SELECT
o.orderno,
to_char(o.orderdate, 'DD-MM-YYYY'),
i.invno
FROM
(
SELECT o.*,
row_number() over (order by to_char(orderdate, 'MMDD')) as rn
FROM orders o
) o, invoices i
WHERE i.invno = o.invno
AND rn = 1;
Or:
SELECT
o.orderno,
to_char(o.orderdate, 'DD-MM-YYYY'),
i.invno
FROM
(
SELECT orderno, orderdate, invno
FROM
(
SELECT o.*,
row_number() over (order by to_char(orderdate, 'MMDD')) as rn
FROM orders o
)
WHERE rn = 1
) o, invoices i
WHERE i.invno = o.invno;
The first looks like it does more work but the execution plans are the same.
SQL Fiddle with your pastebin-supplied query that gets two rows back, and these two that get one.
I need to update a column in a table to the latest date/time combination from another table. How can I get the latest date/time combination from the one table and then update a column with that date in another table?
The two tables I am using are called dbo.DD and dbo.PurchaseOrders. The JOIN between the two tables are dbo.DueDate.XDORD = dbo.PurchaseOrders.PBPO AND dbo.DueDate.XDLINE = dbo.PurchaseOrders.PBSEQ. The columns from dbo.DueDate that I need the latest date/time from are dbo.DueDate.XDCCTD and dbo.DueDate.XDCCTT.
I need to set dbo.PurchaseOrders.PBDUE = dbo.DueDate.XDCURDT.I can't use an ORDER BY statement in the UPDATE statement, so I'm not sure how to do this. I know row_number sometimes works in these situations, but I'm unsure of how to implement.
The general pattern is:
;WITH s AS
(
SELECT
key, -- may be multiple columns
date_col,
rn = ROW_NUMBER() OVER
(
PARTITION BY key -- again, may be multiple columns
ORDER BY date_col DESC
)
FROM dbo.SourceTable
)
UPDATE d
SET d.date_col = s.date_col
FROM dbo.DestinationTable AS d
INNER JOIN s
ON d.key = s.key -- one more time, may need multiple columns here
WHERE s.rn = 1;
I didn't try to map your table names and columns because (a) I didn't get from your word problem which table was the source and which was the destination and (b) those column names look like alphabet soup and I would have screwed them up anyway.
Did seem though that the OP got this specific code working:
;WITH s AS
(
SELECT
XDORD, XDLINE,
XDCURDT,
rn = ROW_NUMBER() OVER
(
PARTITION BY XDORD, XDLINE
ORDER BY XDCCTD DESC, XDCCTT desc
)
FROM dbo.DueDate
)
UPDATE d
SET d.PBDUE = s.XDCURDT
FROM dbo.PurchaseOrders AS d
INNER JOIN s
ON d.PBPO = s.XDORD AND d.PBSEQ = s.XDLINE
WHERE s.rn = 1;