I'm trying to return 7 events from a table, from todays date, and have them in date order:
SELECT ID
FROM table
where ID in (select ID from table
where DATEFIELD >= trunc(sysdate)
order by DATEFIELD ASC)
and rownum <= 7
If I remove the 'order by' it returns the IDs just fine and the query works, but it's not in the right order. Would appreciate any help with this since I can't seem to figure out what I'm doing wrong!
(edit) for clarification, I was using this before, and the order returned was really out:
select ID
from TABLE
where DATEFIELD >= trunc(sysdate)
and rownum <= 7
order by DATEFIELD
Thanks
The values for the ROWNUM "function" are applied before the ORDER BY is processed. That why it doesn't work the way you used it (See the manual for a similar explanation)
When limiting a query using ROWNUM and an ORDER BY is involved, the ordering must be done in an inner select and the limit must be applied in the outer select:
select *
from (
select *
from table
where datefield >= trunc(sysdate)
order by datefield ASC
)
where rownum <= 7
You cannot use order by in where id in (select id from ...) kind of subquery. It wouldn't make sense anyway. This condition only checks if id is in subquery. If it affects the order of output, it's only incidental. With different data query execution plan might be different and output order would be different as well. Use explicit order by at the end of the main query.
It is well known 'feature' of Oracle that rownum doesn't play nice with order by. See http://www.adp-gmbh.ch/ora/sql/examples/first_rows.html for more information. In your case you should use something like:
SELECT ID
FROM (select ID, row_number() over (order by DATEFIELD ) r
from table
where DATEFIELD >= trunc(sysdate))
WHERE r <= 7
See also:
http://www.orafaq.com/faq/how_does_one_select_the_top_n_rows_from_a_table
http://www.oracle.com/technetwork/issue-archive/2006/06-sep/o56asktom-086197.html
http://asktom.oracle.com/pls/asktom/f?p=100:11:507524690399301::::P11_QUESTION_ID:127412348064
See also other similar questions on SO, eg.:
Oracle SELECT TOP 10 records
Oracle/SQL - Select specified range of sequential records
Your outer query cant "see" the ORDER in the inner query and in this case the order in the inner doesn't make sense because it (the inner) is only being used to create a subset of data that will be used on the WHERE of the outer one, so the order of this subset doesn't matter.
maybe if you explain better what you want to do, we can help you
ORDER BY CLAUSE IN Subqueries:
the order by clause is not allowed inside a subquery, with the exception of the inline views. If attempt to include an ORDER BY clause, you receive an error message
An inline View is a query at the from clause.
SELECT t.*
FROM (SELECT id, name FROM student) t
Related
I'm creating PREDICATE system for my application.
Please see image that I already
I have a question how can I select rows in SQL with latest date "Taken On" column tables for each "QuizESId" columns, before that I am understand how to select it but it only using one table, I learn from this
select rows in sql with latest date for each ID repeated multiple times
Here is what I have already tried
SELECT tt.*
FROM myTable tt
INNER JOIN
(SELECT ID, MAX(Date) AS MaxDateTime
FROM myTable
GROUP BY ID) groupedtt ON tt.ID = groupedtt.ID
AND tt.Date = groupedtt.MaxDateTime
What I am confused about here is how can I select from 3 tables, I hope you can guide me, of course I need a solution with good query and efficient performance.
Thanks
This is for SQL Server (you didn't specify exactly what RDBMS you're using):
if you want to get the "latest row for each QuizId" - this sounds like you need a CTE (Common Table Expression) with a ROW_NUMBER() value - something like this (updated: you obviously want to "partition" not just by QuizId, but also by UserName):
WITH BaseData AS
(
SELECT
mAttempt.Id AS Id,
mAttempt.QuizModelId AS QuizId,
mAttempt.StartedAt AS StartsOn,
mUser.UserName,
mDetail.Score AS Score,
RowNum = ROW_NUMBER() OVER (PARTITION BY mAttempt.QuizModelId, mUser.UserName
ORDER BY mAttempt.TakenOn DESC)
FROM
UserQuizAttemptModels mAttempt
INNER JOIN
AspNetUsers mUser ON mAttempt.UserId = muser.Id
INNER JOIN
QuizAttemptDetailModels mDetail ON mDetail.UserQuizAttemptModelId = mAttempt.Id
)
SELECT *
FROM BaseData
WHERE QuizId = 10053
AND RowNum = 1
The BaseData CTE basically selects the data (as you did) - but it also adds a ROW_NUMBER() column. This will "partition" your data into groups of data - based on the QuizModelId - and it will number all the rows inside each data group, starting at 1, and ordered by the second condition - the ORDER BY clause. You said you want to order by "Taken On" date - but there's no such date visible in your query - so I just guessed it might be on the UserQuizAttemptModels table - change and adapt as needed.
Now you can select from that CTE with your original WHERE condition - and you specify, that you want only the first row for each data group (for each "QuizId") - the one with the most recent "Taken On" date value.
I have a table like as shown below
What I would like to do is get the minimum of each subject. Though I am able to do this with row_number function, I would like to do this with groupby and min() approach. But it doesn't work.
row_number approach - works fine
SELECT * FROM (select subject_id,value,id,min_time,max_time,time_1,
row_number() OVER (PARTITION BY subject_id ORDER BY value) AS rank
from table A) WHERE RANK = 1
min() approach - doesn't work
select subject_id,id,min_time,max_time,time_1,min(value) from table A
GROUP BY SUBJECT_ID,id
As you can see just the two columns (subject_id and id) is enough to group the items together. They will help differentiate the group. But why am I not able to use the other columns in select clause. If I use the other columns, I may not get the expected output because time_1 has different values.
I expect my output to be like as shown below
In BigQuery you can use aggregation for this:
SELECT ARRAY_AGG(a ORDER BY value LIMIT 1)[SAFE_OFFSET(1)].*
FROM table A
GROUP BY SUBJECT_ID;
This uses ARRAY_AGG() to aggregate each record (the a in the argument list). ARRAY_AGG() allows you to order the result (by value) and to limit the size of the array. The latter is important for performance.
After you concatenate the arrays, you want the first element. The .* transforms the record referred to by a to the component columns.
I'm not sure why you don't want to use ROW_NUMBER(). If the problem is the lingering rank column, you an easily remove it:
SELECT a.* EXCEPT (rank)
FROM (SELECT a.*,
ROW_NUMBER() OVER (PARTITION BY subject_id ORDER BY value) AS rank
FROM A
) a
WHERE RANK = 1;
Are you looking for something like below-
SELECT
A.subject_id,
A.id,
A.min_time,
A.max_time,
A.time_1,
A.value
FROM table A
INNER JOIN(
SELECT subject_id, MIN(value) Value
FROM table
GROUP BY subject_id
) B ON A.subject_id = B.subject_id
AND A.Value = B.Value
If you do not required to select Time_1 column's value, this following query will work (As I can see values in column min_time and max_time is same for the same group)-
SELECT
A.subject_id,A.id,A.min_time,A.max_time,
--A.time_1,
MIN(A.value)
FROM table A
GROUP BY
A.subject_id,A.id,A.min_time,A.max_time
Finally, the best approach is if you can apply something like CAST(Time_1 AS DATE) on your time column. This will consider only the date part regardless of the time part. The query will be
SELECT
A.subject_id,A.id,A.min_time,A.max_time,
CAST(A.time_1 AS DATE) Time_1,
MIN(A.value)
FROM table A
GROUP BY
A.subject_id,A.id,A.min_time,A.max_time,
CAST(A.time_1 AS DATE)
-- Make sure the syntax of CAST AS DATE
-- in BigQuery is as I written here or bit different.
Below is for BigQuery Standard SQL and is most efficient way for such cases like in your question
#standardSQL
SELECT AS VALUE ARRAY_AGG(t ORDER BY value LIMIT 1)[OFFSET(0)]
FROM `project.dataset.table` t
GROUP BY subject_id
Using ROW_NUMBER is not efficient and in many cases lead to Resources exceeded error.
Note: self join is also very ineffective way of achieving your objective
A bit late to the party, but here is a cte-based approach which made sense to me:
with mins as (
select subject_id, id, min(value) as min_value
from table
group by subject_id, id
)
select distinct t.subject_id, t.id, t.time_1, t.min_time, t.max_time, m.min_value
from table t
join mins m on m.subject_id = t.subject_id and m.id = t.id
I am wondering in particular about PostgreSQL. Given the following contrived example:
SELECT name FROM
(SELECT name FROM people WHERE age >= 18 ORDER BY age DESC) p
LIMIT 10
Are the names returned from the outer query guaranteed to be be in the order they were for the inner query?
No, put the order by in the outer query:
SELECT name FROM
(SELECT name, age FROM people WHERE age >= 18) p
ORDER BY p.age DESC
LIMIT 10
The inner (sub) query returns a result-set. If you put the order by there, then the intermediate result-set passed from the inner (sub) query, to the outer query, is guaranteed to be ordered the way you designate, but without an order by in the outer query, the result-set generated by processing that inner query result-set, is not guaranteed to be sorted in any way.
For simple cases, #Charles query is most efficient.
More generally, you can use the window function row_number() to carry any order you like to the main query, including:
order by columns not in the SELECT list of the subquery and thus not reproducible
arbitrary ordering of peers according to ORDER BY criteria. Postgres will reuse the same arbitrary order in the window function within the subquery. (But not truly random order from random() for instance!)
If you don't want to preserve arbitrary sort order of peers from the subquery, use rank() instead.
This may also be generally superior with complex queries or multiple query layers:
SELECT p.name
FROM (
SELECT name, row_number() OVER (ORDER BY <same order by criteria>) AS rn
FROM people
WHERE age >= 18
ORDER BY <any order by criteria>
) p
ORDER BY p.rn
LIMIT 10;
The are not guaranteed to be in the same order, though when you run it you might see that it is generally follows the order.
You should place the order by on the main query
SELECT name FROM
(SELECT name FROM people WHERE age >= 18) p
ORDER BY p.age DESC LIMIT 10
In Oracle 9.2.0.8, I need to return a record set where a particular field (LAB_SEQ) is at a maximum (it is a sequential VARCHAR array '0001', '0002', etc.) for each of another field (WO_NUM). To select the maximum, I am attempting to order in descending order and select the first row. Everything I can find on StackOverflow suggests that the only way to do this is with a correlated subquery. Then I use this maximum in the WHERE clause of the outer query to get the row I want for each WO_NUM:
SELECT lt.WO_NUM, lt.EMP_NUM, lt.LAB_END_DATE, lt.LAB_END_TIME
FROM LAB_TIM lt WHERE lt.LAB_SEQ = (
SELECT LAB_SEQ FROM (
SELECT lab.LAB_SEQ FROM LAB_TIM lab WHERE lab.CCN='1' AND MAS_LOC='1'
AND lt.WO_NUM = lab.WO_NUM ORDER BY ROWNUM DESC
) WHERE ROWNUM=1
)
However, this returns an invalid identifier for lt.WO_NUM error. Research suggests that ORacle 8 only allows correlated subqueries one level deep, and suggests rewriting to avoid the subquery - something which discussion of selecting maximums suggests can't be done. Any help getting this statement to execute would be greatly appreciated.
Your correlated subquery would need to be something like
SELECT lt.WO_NUM, lt.EMP_NUM, lt.LAB_END_DATE, lt.LAB_END_TIME
FROM LAB_TIM lt WHERE lt.LAB_SEQ = (
SELECT max(lab.LAB_SEQ)
FROM LAB_TIM lab
WHERE lab.CCN='1' AND MAS_LOC='1'
AND lt.WO_NUM = lab.WO_NUM
)
Since you are on Oracle 9.2, it will probably be more efficient to use a correlated subquery. I'm not sure what the predicates lab.CCN='1' AND MAS_LOC='1' are doing in your current query so I'm not quite sure how to translate them into the analytic function approach. Is the combination of LAB_SEQ and WO_NUM not unique in LAB_TIM? Do you need to add in the predicates on CCN and MAS_LOC in order to get a single unique row for every WO_NUM? Or are you using those predicates to decrease the number of rows in your output? The basic approach will be something like
SELECT *
FROM (SELECT lt.WO_NUM,
lt.EMP_NUM,
lt.LAB_END_DATE,
lt.LAB_END_TIME,
rank() over (partition by wo_num
order by lab_seq desc) rnk
FROM LAB_TIM lt)
WHERE rnk = 1
but it's not clear to me whether CCN and MAS_LOC need to be added to the ORDER BY clause in the analytic function or whether they need to be added to the WHERE clause.
This is one case where a correlated subquery is better, particularly if you have indexes on the table. However, it should be possible to rewrite correlated subqueries as joins.
I think the following is equivalent, without the correlated subquery:
SELECT lt.WO_NUM, lt.EMP_NUM, lt.LAB_END_DATE, lt.LAB_END_TIME
FROM (select *, rownum as r
from LAB_TIM lt
) lt join
(select wo_num, max(r) as maxrownum
from (select LAB_SEQ, wo_num, rownum as r
from LAB_TIM lt
where lab.CCN = '1' AND MAS_LOC = '1'
)
) ltsum
on lt.wo_num = ltsum.wo_num and
lt.r = ltsum.maxrownum
I'm a little unsure about how Oracle works with rownums in things like ORDER BY.
How can I order the data and then filter it in TSQL (SQL Server)?
I've tried something like this:
SELECT [Job].*,
ROW_NUMBER() OVER (ORDER BY [Job].[Date]) AS RowNum
FROM [Job]
ORDER BY Rank
WHERE RowNum >= #Start AND RowNum < #End
Doesn't work. I also tried to use a subquery, which throws:
The ORDER BY clause is invalid in
views, inline functions, derived
tables, subqueries, and common table
expressions, unless TOP or FOR XML is
also specified.
I don't want to use TOP or FOR XML.
How to solve this?
Use a CTE. Note, the "inner" ORDER BY in this case is implied by the ROW_NUMBER/OVER.
;WITH cBase AS
(
SELECT
[Job].*,
ROW_NUMBER() OVER (ORDER BY [Job].[Date]) AS RowNum
FROM
[Job]
)
SELECT
*
FROM
cBase
WHERE
RowNum >= #Start AND RowNum < #End
--ORDER BY
--output order
Edit:
Your search between #Start and #End is on the sequence generated by the ROW_NUMBER on date.
Rank has no relation to this sequence. Rank (assuming it's a column in the table) will be ignored because your sequence is on Date. You don't need to sort on it.
If "rank" is actually "RowNum" then you still don't need an "inner" sort because it's a set operation. You'll need it on the outermost sort though.
If rank is a secondary sort on Date then use this:
ROW_NUMBER() OVER (ORDER BY [Job].[Date], [Job].[Rank]) AS RowNum