I am trying to create some sql to calculate the worth of a users inventory and have manage to get it to work up to the final step.
SELECT DISTINCT ON (pricing_cards.card_id)
(inventory_cards.nonfoil * pricing_cards.nonfoil) + (inventory_cards.foil * pricing_cards.foil) as x
FROM inventory_cards
INNER JOIN pricing_cards ON pricing_cards.card_id = inventory_cards.card_id
WHERE inventory_cards.user_id = 1
ORDER BY pricing_cards.card_id, pricing_cards.date DESC;
The code above bring back a single column that has the correct calculation for card. I now need to sum this column together but keep getting errors when I try to sum it.
Adding SUM((inventory_cards.nonfoil * pricing_cards.nonfoil) + (inventory_cards.foil * pricing_cards.foil)) throws the following error
ERROR: column "pricing_cards.card_id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 6: ORDER BY pricing_cards.card_id, pricing_cards.date DESC;
Adding GROUP BY pricing_cards.card_id, pricing_cards.date seems to fix the errors but is returning the same column of calculated values.
so:
SELECT DISTINCT ON (pricing_cards.card_id)
SUM((inventory_cards.nonfoil * pricing_cards.nonfoil) + (inventory_cards.foil * pricing_cards.foil)) as x
FROM inventory_cards
INNER JOIN pricing_cards ON pricing_cards.card_id = inventory_cards.card_id
WHERE inventory_cards.user_id = 1
GROUP BY pricing_cards.card_id, pricing_cards.date
ORDER BY pricing_cards.card_id, pricing_cards.date DESC;
Returns:
x
0.71
29.92
25.67
171.20
0.32
0.26
I suggest you use a subquery to get the latest pricing data, then join and sum:
SELECT
SUM(inventory_cards.nonfoil * latest_pricing.nonfoil + inventory_cards.foil * latest_pricing.foil)
FROM inventory_cards
INNER JOIN (
SELECT DISTINCT ON (card_id)
card_id, nonfoil, foild
FROM pricing_cards
ORDER BY pricing_cards.card_id, pricing_cards.date DESC
) AS latest_pricing USING (card_id)
WHERE inventory_cards.user_id = 1
For alternatives in the subquery, see also Select first row in each GROUP BY group? and Optimize GROUP BY query to retrieve latest row per user.
Related
I'm using two different data sources in Grafana and need to use the result from each to calculate a percentage. What I need is equivalent to A/B, where A is
SELECT count(id) FROM Logs WHERE $__unixEpochFilter(RequestTimestamp DIV 1000)
from Database 1 and B is
SELECT count(id) FROM Entries WHERE $__unixEpochFilter(RequestTimestamp DIV 1000)
from Database 2. I can create a mixed data source panel and retrieve A and B, but can't find a way to perform an operation on the two results.
You can move the subqueries to the from clause and use cross join:
SELECT l.cnt * 1.0 / e.cnt
FROM (SELECT count(id) as cnt
FROM Logs
WHERE $__unixEpochFilter(RequestTimestamp DIV 1000)
) l CROSS JOIN
(SELECT count(id) as cnt
FROM Entries
WHERE $__unixEpochFilter(RequestTimestamp DIV 1000)
) e
The * 1.0 is because DB2 does integer division.
I have two tables: contracts and contract_descriptions.
On contract_descriptions there is a column named contract_id which is equal on contracts table records.
I am trying to join the latest record on contract_descriptions:
SELECT *
FROM contracts c
LEFT JOIN contract_descriptions d ON d.contract_id = c.contract_id
AND d.date_description =
(SELECT MAX(date_description)
FROM contract_descriptions t
WHERE t.contract_id = c.contract_id)
It works, but is it the performant way to do it? Is there a way to avoid the second SELECT?
You could also alternatively use DISTINCT ON:
SELECT * FROM contracts c LEFT JOIN (
SELECT DISTINCT ON (cd.contract_id) cd.* FROM contract_descriptions cd
ORDER BY cd.contract_id, cd.date_description DESC
) d ON d.contract_id = c.contract_id
DISTINCT ON selects only one row per contract_id while the sort clause cd.date_description DESC ensures that it is always the last description.
Performance depends on many values (for example, table size). In any case, you should compare both approaches with EXPLAIN.
Your query looks okay to me. One typical way to join only n rows by some order from the other table is a lateral join:
SELECT *
FROM contracts c
CROSS JOIN LATERAL
(
SELECT *
FROM contract_descriptions cd
WHERE cd.contract_id = c.contract_id
ORDER BY cd.date_description DESC
FETCH FIRST 1 ROW ONLY
) cdlast;
I would like to do something like this:
CNT=2;
//[edit]
select avg(price) from (
select first :CNT p.Price
from Price p
order by p.Date desc
);
This does not work, Firebird does not allow :cnt as a parameter to FIRST. I need to average the first CNT newest prices. The number 2 changes so it can not be hard-coded.
This can be broken out into a FOR SELECT loop and break when a count is reached. Is that the best way though? Can this be done in a single SQL statement?
Creating the SQL as a string and running it is not the best fit either. It is important that the database compile my SQL statement.
You don't have to use CTE, you can do it directly:
select avg(price) from (
select first :cnt p.Price
from Price p
order by p.Date desc
);
You can use a CTE (Common Table Expression) (see http://www.firebirdsql.org/refdocs/langrefupd21-select.html#langrefupd21-select-cte) to select data before calculate average.
See example below:
with query1 as (
select first 2 p.Price
from Price p
order by p.Date desc
)
select avg(price) from query1
When I run the query (1st Code) below I get 1.37 million random Departure Dates based on the current Arrival Date in the database, this is good news. However when I try to update the database with the 2nd Code query I get an error message(See below) and I don't know why. Can you help?
Msg 116, Level 16, State 1, Line 5 Only one expression can be
specified in the select list when the subquery is not introduced with
EXISTS.
1st Code
SELECT ArrivalDate, DATEADD(day, 1 + RAND(checksum(NEWID()))
* LengthOfStay.LengthofStay, ArrivalDate) AS DepartureDate
FROM Bookings, LengthOfStay
ORDER BY ArrivalDate
2nd Code
USE Occupancy
Update Bookings
Set DepartureDate = (SELECT ArrivalDate, DATEADD(day, 1 + RAND(checksum(NEWID()))*1.5
* LengthOfStay.LengthofStay, ArrivalDate))
FROM LengthOfStay, Bookings
You have several problems:
LengthOfStay, Bookings is a CROSS JOIN (Cartesian product): is this intended
You have 2 columns from the sub query but are trying to update only one
Assuming your CROSS JOIN is intended, you don't need the subquery
UPDATE
B
SET
DepartureDate = DATEADD(day,
1 + RAND(checksum(NEWID()))*1.5 * L.LengthofStay,
B.ArrivalDate)
FROM
LengthOfStay L, Bookings B
It seems you are selecting 2 columns to update 1 column(DepartureDate)
I have the following TSQL query:
SELECT DISTINCT MyTable1.Date
FROM MyTable1
INNER JOIN MyTable2
ON MyTable1.Id = MyTable2.Id
WHERE Name = 'John' ORDER BY MyTable1.Date DESC
It retrieves a long list of Dates, but I only need the first one, the one in the first row.
How can I get it?
Thanks a ton!
In SQL Server you can use TOP:
SELECT TOP 1 MyTable1.Date
FROM MyTable1
INNER JOIN MyTable2
ON MyTable1.Id = MyTable2.Id
WHERE Name = 'John'
ORDER BY MyTable1.Date DESC
If you need to use DISTINCT, then you can use:
SELECT TOP 1 x.Date
FROM
(
SELECT DISTINCT MyTable1.Date
FROM MyTable1
INNER JOIN MyTable2
ON MyTable1.Id = MyTable2.Id
WHERE Name = 'John'
) x
ORDER BY x.Date DESC
Or even:
SELECT MAX(MyTable1.Date)
FROM MyTable1
INNER JOIN MyTable2
ON MyTable1.Id = MyTable2.Id
WHERE Name = 'John'
--ORDER BY MyTable1.Date DESC
There are several options here. You can use TOP(1) as Taryn mentioned. But according to docs for the purposes of limiting the rows returned it is better to use OFFSET and FETCH.
We recommend that you use the OFFSET and FETCH clauses instead of the TOP clause to implement a query paging solution and limit the number of rows sent to a client application.
Using OFFSET and FETCH as a paging solution requires running the query one time for each "page" of data returned to the client application. For example, to return the results of a query in 10-row increments, you must execute the query one time to return rows 1 to 10 and then run the query again to return rows 11 to 20 and so on.
Assuming, the solution for your problem using OFFSET and FETCH approach could be:
SELECT DISTINCT MyTable1.Date
FROM MyTable1
INNER JOIN MyTable2
ON MyTable1.Id = MyTable2.Id
WHERE Name = 'John' ORDER BY MyTable1.Date DESC
OFFSET 0 ROWS
FETCH NEXT 1 ROW ONLY