select
TV.ATTRIBUTE
FROM
TABLE_VALUE TV
WHERE
TV.NUMBERS IN (SELECT MAX(TV1.NUMBERS) FROM TABLE_VALUE TV1
WHERE TV.UNIQUE_ID=TV1.UNIQUE_ID GROUP BY UNIQUE_ID )
I'm not sure exists would help here, because - as you put it - for each unique_id there be many numbers values, and you want to select attribute for highest numbers for that particular unique_id.
exists is useful when you want to check whether something ... well, exists, but that's not the case here.
You do not want EXISTS, instead you can use the RANK or DENSE_RANK analytic functions:
SELECT attribute
FROM (
SELECT attribute,
DENSE_RANK() OVER (PARTITION BY unique_id ORDER BY numbers DESC) AS rnk
FROM table_value
)
WHERE rnk = 1
or use the MAX analytic function:
SELECT attribute
FROM (
SELECT attribute,
numbers,
MAX(numbers) OVER (PARTITION BY unique_id) AS max_numbers
FROM table_value
)
WHERE numbers = max_numbers;
Either option will only read from the table once.
If you really did want to use EXISTS (or IN) then it will be less efficient as you will query the same table twice but you can do it with a HAVING clause:
SELECT tv.attribute
FROM table_value tv
WHERE EXISTS(
SELECT 1
FROM table_value tv1
WHERE tv1.unique_id = tv.unique_id
HAVING MAX(tv1.numbers) = tv.numbers
)
fiddle
I have a table like this
and i want my output to look like this
I need to look at the ID and then take max created date and max completed date for that ID. There is also some cases where completed date is still empty so in that case i just need to look at the max created date. Im not sure how to tackle this, doing a group by doesnt account for my multiple scenarios
Use ROW_NUMBER:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY QUOTE_NUMBER
ORDER BY WORKBOOK_CREATED_DATE DESC) rn
FROM yourTable
)
SELECT *
FROM yourTable
WHERE rn = 1;
In SQL Server, I am attempting to pull the second latest NOTE_ENTRY_DT_TIME (items highlighted in screenshot). With the query written below it still pulls the latest date (I believe it's because of the grouping but the grouping is required to join later). What is the best method to achieve this?
SELECT
hop.ACCOUNT_ID,
MAX(hop.NOTE_ENTRY_DT_TIME) AS latest_noteid
FROM
NOTES hop
WHERE
hop.GEN_YN IS NULL
AND hop.NOTE_ENTRY_DT_TIME < (SELECT MAX(hope.NOTE_ENTRY_DT_TIME)
FROM NOTES hope
WHERE hop.GEN_YN IS NULL)
GROUP BY
hop.ACCOUNT_ID
Data sample in the table:
One of the "easier" ways to get the Nth row in a group is to use a CTE and ROW_NUMBER:
WITH CTE AS(
SELECT Account_ID,
Note_Entry_Dt_Time,
ROW_NUMBER() OVER (PARTITION BY AccountID ORDER BY Note_Entry_Dt_Time DESC) AS RN
FROM dbo.YourTable)
SELECT Account_ID,
Note_Entry_Dt_Time
FROM CTE
WHERE RN = 2;
Of course, if an ACCOUNT_ID only has 1 row, then it will not be returned in the result set.
The OP's statement "The row will not always be 2." from the comments conflicts with their statement "I am attempting to pull the second latest NOTE_ENTRY_DT_TIME" in the question. At a best guess, this means that the OP has rows with the same date, that could be the "latest" date. If so, then would simply need to replace ROW_NUMBER with DENSE_RANK. Their sampple data, however, doesn't suggest this is the case.
You can use window functions:
select *
from (
select
n.*,
row_number() over(partition by account_id order by note_entry_dt_time desc) rn
from notes n
) t
where rn = 2
I am looking to select unique values from a SQL database but I want to make sure that I am selecting only the first duplicate in order of appearance (in my case - date in the hospital, intime col)
You can see the code below.
I am trying to take only the IDs of the first time the patients were hospitalized which correspond to the "intime" col.
I have no absolute way to check that by ordering as I did and by using groupby, SQL will in fact return the id in the same order.
Thank you very much.
WITH ccupatients AS
(SELECT HADM_ID
FROM `physionet-data.mimiciii_clinical.icustays` i
WHERE first_careunit = 'CCU'
ORDER BY intime)
SELECT hadm_id
FROM ccupatients
GROUP BY hadm_id
Use ROW_NUMBER() if your RDBMS supports it: this works by ranking records by increasing intime within groups of records having the same ham_id, and then filtering in the outer query on the top record per group:
SELECT hadm_id
FROM (
SELECT hadm_id, ROW_NUMBER() OVER(PARTITION BY hadm_id ORDER BY intime) rn
FROM `physionet-data.mimiciii_clinical`.icustays
WHERE first_careunit = 'CCU'
) x
WHERE rn = 1
If you RDBMS does not support window functions such as ROW_NUMBER(), another option is to use a NOT EXISTS condition with a correlated subquery:
SELECT hadm_id
FROM `physionet-data.mimiciii_clinical`.icustays i
WHERE
first_careunit = 'CCU'
AND NOT EXISTS (
SELECT 1
FROM `physionet-data.mimiciii_clinical`.icustays i1
WHERE
i1.first_careunit = 'CCU'
AND i1.hadm_id = i.hadm_id
AND i1.intime < i.intime
)
Title says it all, why can't I use a windowed function in a where clause in SQL Server?
This query makes perfect sense:
select id, sales_person_id, product_type, product_id, sale_amount
from Sales_Log
where 1 = row_number() over(partition by sales_person_id, product_type, product_id order by sale_amount desc)
But it doesn't work. Is there a better way than a CTE/Subquery?
EDIT
For what its worth this is the query with a CTE:
with Best_Sales as (
select id, sales_person_id, product_type, product_id, sale_amount, row_number() over (partition by sales_person_id, product_type, product_id order by sales_amount desc) rank
from Sales_log
)
select id, sales_person_id, product_type, product_id, sale_amount
from Best_Sales
where rank = 1
EDIT
+1 for the answers showing with a subquery, but really I'm looking for the reasoning behind not being able to use windowing functions in where clauses.
why can't I use a windowed function in a where clause in SQL Server?
One answer, though not particularly informative, is because the spec says that you can't.
See the article by Itzik Ben Gan - Logical Query Processing: What It Is And What It Means to You and in particular the image here. Window functions are evaluated at the time of the SELECT on the result set remaining after all the WHERE/JOIN/GROUP BY/HAVING clauses have been dealt with (step 5.1).
really I'm looking for the reasoning behind not being able to use
windowing functions in where clauses.
The reason that they are not allowed in the WHERE clause is that it would create ambiguity. Stealing Itzik Ben Gan's example from High-Performance T-SQL Using Window Functions (p.25)
Suppose your table was
CREATE TABLE T1
(
col1 CHAR(1) PRIMARY KEY
)
INSERT INTO T1 VALUES('A'),('B'),('C'),('D'),('E'),('F')
And your query
SELECT col1
FROM T1
WHERE ROW_NUMBER() OVER (ORDER BY col1) <= 3
AND col1 > 'B'
What would be the right result? Would you expect that the col1 > 'B' predicate ran before or after the row numbering?
There is no need for CTE, just use the windowing function in a subquery:
select id, sales_person_id, product_type, product_id, sale_amount
from
(
select id, sales_person_id, product_type, product_id, sale_amount,
row_number() over(partition by sales_person_id, product_type, product_id order by sale_amount desc) rn
from Sales_Log
) sl
where rn = 1
Edit, moving my comment to the answer.
Windowing functions are not performed until the data is actually selected which is after the WHERE clause. So if you try to use a row_number in a WHERE clause the value is not yet assigned.
"All-at-once operation" means that all expressions in the same
logical query process phase are evaluated logically at the same time.
And great chapter Impact on Window Functions:
Suppose you have:
CREATE TABLE #Test ( Id INT) ;
INSERT INTO #Test VALUES ( 1001 ), ( 1002 ) ;
SELECT Id
FROM #Test
WHERE Id = 1002
AND ROW_NUMBER() OVER(ORDER BY Id) = 1;
All-at-Once operations tell us these two conditions evaluated logically at the same point of time. Therefore, SQL Server can
evaluate conditions in WHERE clause in arbitrary order, based on
estimated execution plan. So the main question here is which condition
evaluates first.
Case 1:
If ( Id = 1002 ) is first, then if ( ROW_NUMBER() OVER(ORDER BY Id) = 1 )
Result: 1002
Case 2:
If ( ROW_NUMBER() OVER(ORDER BY Id) = 1 ), then check if ( Id = 1002 )
Result: empty
So we have a paradox.
This example shows why we cannot use Window Functions in WHERE clause.
You can think more about this and find why Window Functions are
allowed to be used just in SELECT and ORDER BY clauses!
Addendum
Teradata supports QUALIFY clause:
Filters results of a previously computed ordered analytical function according to user‑specified search conditions.
SELECT Id
FROM #Test
WHERE Id = 1002
QUALIFY ROW_NUMBER() OVER(ORDER BY Id) = 1;
Snowflake - Qualify
QUALIFY does with window functions what HAVING does with aggregate functions and GROUP BY clauses.
In the execution order of a query, QUALIFY is therefore evaluated after window functions are computed. Typically, a SELECT statement’s clauses are evaluated in the order shown below:
From
Where
Group by
Having
Window
QUALIFY
Distinct
Order by
Limit
Databricks - QUALIFY clasue
Filters the results of window functions. To use QUALIFY, at least one window function is required to be present in the SELECT list or the QUALIFY clause.
You don't necessarily need to use a CTE, you can query the result set after using row_number()
select row, id, sales_person_id, product_type, product_id, sale_amount
from (
select
row_number() over(partition by sales_person_id,
product_type, product_id order by sale_amount desc) AS row,
id, sales_person_id, product_type, product_id, sale_amount
from Sales_Log
) a
where row = 1
It's an old thread, but I'll try to answer specifically the question expressed in the topic.
Why no windowed functions in where clauses?
SELECT statement has following main clauses specified in keyed-in order:
SELECT DISTINCT TOP list
FROM JOIN ON / APPLY / PIVOT / UNPIVOT
WHERE
GROUP BY WITH CUBE / WITH ROLLUP
HAVING
ORDER BY
OFFSET-FETCH
Logical Query Processing Order, or Binding Order, is conceptual interpretation order, it defines the correctness of the query. This order determines when the objects defined in one step are made available to the clauses in subsequent steps.
----- Relational result
1. FROM
1.1. ON JOIN / APPLY / PIVOT / UNPIVOT
2. WHERE
3. GROUP BY
3.1. WITH CUBE / WITH ROLLUP
4. HAVING
---- After the HAVING step the Underlying Query Result is ready
5. SELECT
5.1. SELECT list
5.2. DISTINCT
----- Relational result
----- Non-relational result (a cursor)
6. ORDER BY
7. TOP / OFFSET-FETCH
----- Non-relational result (a cursor)
For example, if the query processor can bind to (access) the tables or views defined in the FROM clause, these objects and their columns are made available to all subsequent steps.
Conversely, all clauses preceding the SELECT clause cannot reference any column aliases or derived columns defined in SELECT clause. However, those columns can be referenced by subsequent clauses such as the ORDER BY clause.
OVER clause determines the partitioning and ordering of a row set before the associated window function is applied. That is, the OVER clause defines a window or user-specified set of rows within an Underlying Query Result set and window function computes result against that window.
Msg 4108, Level 15, State 1, …
Windowed functions can only appear in the SELECT or ORDER BY clauses.
The reason behind is because the way how Logical Query Processing works in T-SQL. Since the underlying query result is established only when logical query processing reaches the SELECT step 5.1. (that is, after processing the FROM, WHERE, GROUP BY and HAVING steps), window functions are allowed only in the SELECT and ORDER BY clauses of the query.
Note to mention, window functions are still part of relational layer even Relational Model doesn't deal with ordered data. The result after the SELECT step 5.1. with any window function is still relational.
Also, speaking strictly, the reason why window function are not allowed in the WHERE clause is not because it would create ambiguity, but because the order how Logical Query Processing processes SELECT statement in T-SQL.
Links: here, here and here
Finally, there's the old-fashioned, pre-SQL Server 2005 way, with a correlated subquery:
select *
from Sales_Log sl
where sl.id = (
Select Top 1 id
from Sales_Log sl2
where sales_person_id = sl.sales_person_id
and product_type = sl.product_type
and product_id = sl.product_id
order by sale_amount desc
)
I give you this for completeness, merely.
Basically first "WHERE" clause condition is read by sql and the same column/value id looked into the table but in table row_num=1 is not there still. Hence it will not work.
Thats the reason we will use parentheses first and after that we will write the WHERE clause.
Yes unfortunately when you do a windowed function SQL gets mad at you even if your where predicate is legitimate. You make a cte or nested select having the value in your select statement, then reference your CTE or nested select with that value later. Simple example that should be self explanatory. If you really HATE cte's for some performance issue on doing a large data set you can always drop to temp table or table variable.
declare #Person table ( PersonID int identity, PersonName varchar(8));
insert into #Person values ('Brett'),('John');
declare #Orders table ( OrderID int identity, PersonID int, OrderName varchar(8));
insert into #Orders values (1, 'Hat'),(1,'Shirt'),(1, 'Shoes'),(2,'Shirt'),(2, 'Shoes');
--Select
-- p.PersonName
--, o.OrderName
--, row_number() over(partition by o.PersonID order by o.OrderID)
--from #Person p
-- join #Orders o on p.PersonID = o.PersonID
--where row_number() over(partition by o.PersonID order by o.orderID) = 2
-- yields:
--Msg 4108, Level 15, State 1, Line 15
--Windowed functions can only appear in the SELECT or ORDER BY clauses.
;
with a as
(
Select
p.PersonName
, o.OrderName
, row_number() over(partition by o.PersonID order by o.OrderID) as rnk
from #Person p
join #Orders o on p.PersonID = o.PersonID
)
select *
from a
where rnk >= 2 -- only orders after the first one.