A Relational database table holds the information of Insurance details, say id and amount. Table consists of millions of records. requirement is to fetch top 5 records with max amount without using order by clause.
A solution I could think of is to use the temp table to maintain the max 5 records and update these entries each time the main table is updated but would like to know if there are better solution to above problem ?
An efficient way is to put an index on amount desc and use order by. Something like:
select t.*
from t
order by t.amount desc
fetch first 5 rows only; -- or however your database does this
This should be quite efficient.
You can try using analytic functions (example below), but you still have to order at some stage
select id,
amount
from (select id,
amount,
row_number() over (order by amount desc nulls last) as rn
from t)
where rn<=5;
Data I have a table in Access that has a Part Number and PriceYr and Price associated to each Part Number.There are over 10,000 records and the PartNumber are repeated and has different PriceYr and Price associated to it. However, I need a query to just find the 5 most recent price and date associated with it.
I tried using MAX(PriceYr) however, it only returns 1 most recent record for each PartNumber.
I also tried the following query but it doesn't seem to work.
SELECT Catalogs.PartNumber,Catalogs.PriceYr, Catalogs.Price FROM Catalogs
WHERE Catalogs.PriceYr in
(SELECT TOP 5 Catalogs.PriceYr
FROM Catalogs as Temp
WHERE Temp.PartNumber = Catalogs.PartNumber
ORDER By Catalogs.PriceYr DESC)
Any help will be greatly appreciated. Thank you.
Desired Result that i am trying to get.
Consider a correlated count subquery to filter by a rank variable. Right now, you pull top 5 overall on matching PartNumber not per PartNumber.
SELECT main.*
FROM
(SELECT c.PartNumber, c.PriceYr, c.Price,
(SELECT Count(*)
FROM Catalogs AS Temp
WHERE Temp.PartNumber = c.PartNumber
AND Temp.PriceYr >= c.PriceYr) As rank
FROM Catalogs c
) As main
WHERE main.rank <= 5
MAX() is an aggregating function, meaning that it groups all the data and takes the maximal value in the specified column. You need to use a GROUP BY statement to prevent the query from grouping the whole dataset in a single row.
On the other hand, your query seems to needlessly use a subquery. The following query should work quite fine :
SELECT TOP 5 c.PartNumber, c.PriceYr, c.Price
FROM Catalogs c
ORDER BY c.PriceYr DESC
WHERE c.PartNumber = #partNumber -- if you want the query to
-- work on a specific part number
(please post a table creation query to make sure this example works)
I have a big table which has 700 millions of rows and dozens of columns. I need it to carry out a left join operation as the left table.
However, since it is so large, the time consumption is beyond affordable. So I'd like to split into few smaller tables and carry out the task in multiprocessing manner.
I know there is SSIS package is available for this, but I am constrained not to use it.
Also, I know it is a easy way to add a row id to each of the rows, but unfortunately, I cannot make change to the table.
So, may I know how to achieve my goal?
Many thanks.
Using CTE and row_number()
;WITH cte_tbl AS
(
SELECT *,
ROW_NUMBER() OVER (ORDER BY [First Name]) AS RowNumber
FROM your_table
)
SELECT * FROM cte_tbl
WHERE RowNumber < 100
You can fetch records for any range.
Use fetch-offset if you need certain number of rows using sql-script.
like this:
SELECT First Name + ' ' + Last Name FROM big_table ORDER BY First Name OFFSET 15 ROWS;
SELECT First Name + ' ' + Last Name FROM big_table ORDER BY First Name OFFSET 10 ROWS FETCH NEXT 5 ROWS ONLY;
Create a #temp table, and insert a subset of the records into it, then join to the #temp table. You can create an additional ID column in the #temp table as well for your needs.
I want to return the last report of a given range of units. The last report will be identified by its time of creation. Therefore, the result would be a collection of last reports for a given range of units. I do not want to use a bunch of SELECT statements e.g.:
SELECT * FROM reports WHERE unit_id = 9999 ORDER BY time desc LIMIT 1
SELECT * FROM reports WHERE unit_id = 9998 ORDER BY time desc LIMIT 1
...
I initially tried this (but already knew it wouldn't work because it will only return 1 report):
'SELECT reports.* FROM reports INNER JOIN units ON reports.unit_id = units.id WHERE units.account_id IS NOT NULL AND units.account_id = 4 ORDER BY time desc LIMIT 1'
So I am looking for some kind of solution using subqueries or derived tables, but I can't just seem to figure out how to do it properly:
'SELECT reports.* FROM reports
WHERE id IN
(
SELECT id FROM reports
INNER JOIN units ON reports.unit_id = units.id
ORDER BY time desc
LIMIT 1
)
Any solution to do this with subqueries or derived tables?
The simple way to do this in Postgres uses distinct on:
select distinct on (unit_id) r.*
from reports r
order by unit_id, time desc;
This construct is specific to Postgres and databases that use its code base. It the expression distinct on (unit_id) says "I want to keep only one row for each unit_id". The row chosen is the first row encountered with that unit_id based on the order by clause.
EDIT:
Your original query would be, assuming that id increases along with the time field:
SELECT r.*
FROM reports r
WHERE id IN (SELECT max(id)
FROM reports
GROUP BY unit_id
);
You might also try this as a not exists:
select r.*
from reports r
where not exists (select 1
from reports r2
where r2.unit_id = r.unit_id and
r2.time > r.time
);
I thought the distinct on would perform well. This last version (and maybe the previous) would really benefit from an index on reports(unit_id, time).
What is the most efficient way to read the last row with SQL Server?
The table is indexed on a unique key -- the "bottom" key values represent the last row.
If you're using MS SQL, you can try:
SELECT TOP 1 * FROM table_Name ORDER BY unique_column DESC
select whatever,columns,you,want from mytable
where mykey=(select max(mykey) from mytable);
You'll need some sort of uniquely identifying column in your table, like an auto-filling primary key or a datetime column (preferably the primary key). Then you can do this:
SELECT * FROM table_name ORDER BY unique_column DESC LIMIT 1
The ORDER BY column tells it to rearange the results according to that column's data, and the DESC tells it to reverse the results (thus putting the last one first). After that, the LIMIT 1 tells it to only pass back one row.
If some of your id are in order, i am assuming there will be some order in your db
SELECT * FROM TABLE WHERE ID = (SELECT MAX(ID) FROM TABLE)
I think below query will work for SQL Server with maximum performance without any sortable column
SELECT * FROM table
WHERE ID not in (SELECT TOP (SELECT COUNT(1)-1
FROM table)
ID
FROM table)
Hope you have understood it... :)
I tried using last in sql query in SQl server 2008 but it gives this err:
" 'last' is not a recognized built-in function name."
So I ended up using :
select max(WorkflowStateStatusId) from WorkflowStateStatus
to get the Id of the last row.
One could also use
Declare #i int
set #i=1
select WorkflowStateStatusId from Workflow.WorkflowStateStatus
where WorkflowStateStatusId not in (select top (
(select count(*) from Workflow.WorkflowStateStatus) - #i ) WorkflowStateStatusId from .WorkflowStateStatus)
You can use last_value: SELECT LAST_VALUE(column) OVER (PARTITION BY column ORDER BY column)...
I test it at one of my databases and it worked as expected.
You can also check de documentation here: https://msdn.microsoft.com/en-us/library/hh231517.aspx
OFFSET and FETCH NEXT are a feature of SQL Server 2012 to achieve SQL paging while displaying results.
The OFFSET argument is used to decide the starting row to return rows from a result and FETCH argument is used to return a set of number of rows.
SELECT *
FROM table_name
ORDER BY unique_column desc
OFFSET 0 Row
FETCH NEXT 1 ROW ONLY
SELECT TOP 1 id from comission_fees ORDER BY id DESC
In order to retrieve the last row of a table for MS SQL database 2005, You can use the following query:
select top 1 column_name from table_name order by column_name desc;
Note: To get the first row of the table for MS SQL database 2005, You can use the following query:
select top 1 column_name from table_name;
If you don't have any ordered column, you can use the physical id of each lines:
SELECT top 1 sys.fn_PhysLocFormatter(%%physloc%%) AS [File:Page:Slot],
T.*
FROM MyTable As T
order by sys.fn_PhysLocFormatter(%%physloc%%) DESC
SELECT * from Employees where [Employee ID] = ALL (SELECT MAX([Employee ID]) from Employees)
This is how you get the last record and update a field in Access DB.
UPDATE compalints SET tkt = addzone &'-'& customer_code &'-'& sn where sn in (select max(sn) from compalints )
If you have a Replicated table, you can have an Identity=1000 in localDatabase and Identity=2000 in the clientDatabase, so if you catch the last ID you may find always the last from client, not the last from the current connected database.
So the best method which returns the last connected database is:
SELECT IDENT_CURRENT('tablename')
Well I'm not getting the "last value" in a table, I'm getting the Last value per financial instrument. It's not the same but I guess it is relevant for some that are looking to look up on "how it is done now". I also used RowNumber() and CTE's and before that to simply take 1 and order by [column] desc. however we nolonger need to...
I am using SQL server 2017, we are recording all ticks on all exchanges globally, we have ~12 billion ticks a day, we store each Bid, ask, and trade including the volumes and the attributes of a tick (bid, ask, trade) of any of the given exchanges.
We have 253 types of ticks data for any given contract (mostly statistics) in that table, the last traded price is tick type=4 so, when we need to get the "last" of Price we use :
select distinct T.contractId,
LAST_VALUE(t.Price)over(partition by t.ContractId order by created ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)
from [dbo].[Tick] as T
where T.TickType=4
You can see the execution plan on my dev system it executes quite efficient, executes in 4 sec while the exchange import ETL is pumping data into the table, there will be some locking slowing me down... that's just how live systems work.
It is very simple
select top 10 * from TableName order by 1 desc
SELECT * FROM TABLE WHERE ID = (SELECT MAX(ID) FROM TABLE)
I am pretty sure that it is:
SELECT last(column_name) FROM table
Becaause I use something similar:
SELECT last(id) FROM Status