i am having table having 23 records , I am trying to get total count of record and last record also in single query. something like that
select count(*) ,(m order by createdDate) from music m ;
is there any way to pull this out only last record as well as total count in PostgreSQL.
This can be done using window functions
select *
from (
select m.*,
row_number() over (order by createddate desc) as rn,
count(*) over () as total_count
from music
) t
where rn = 1;
Another option would be to use a scalar sub-query and combine it with a limit clause:
select *,
(select count(*) from order_test.orders) as total_count
from music
order by createddate desc
limit 1;
Depending on the indexes, your memory configuration and the table definition might be faster then the two window functions.
No, it's not not possible to do what is being asked, sql does not function that way, the second you ask for a count () sql changes the level of your data to an aggregation. The only way to do what you are asking is to do a count() and order by in a separate query.
Another solution using windowing functions and no subquery:
SELECT DISTINCT count(*) OVER w, last_value(m) OVER w
FROM music m
WINDOW w AS (ORDER BY date DESC RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING);
The point here is that last_value applies on partitions defined by windows and not on groups defined by GROUP BY.
I did not perform any test but I suspect my solution to be the less effective amongst the three already posted. But it is also the closest to your example query so far.
Related
I have one table where multiple records inserted for each group of product. Now, I want to extract (SELECT) only the last entries. For more, see the screenshot. The yellow highlighted records should be return with select query.
The HAVING MAX and HAVING MIN clause for the ANY_VALUE function is now in preview
HAVING MAX and HAVING MIN were just introduced for some aggregate functions - https://cloud.google.com/bigquery/docs/release-notes#February_06_2023
with them query can be very simple - consider below approach
select any_value(t having max datetime).*
from your_table t
group by t.id, t.product
if applied to sample data in your question - output is
You might consider below as well
SELECT *
FROM sample_table
QUALIFY DateTime = MAX(DateTime) OVER (PARTITION BY ID, Product);
If you're more familiar with an aggregate function than a window function, below might be an another option.
SELECT ARRAY_AGG(t ORDER BY DateTime DESC LIMIT 1)[SAFE_OFFSET(0)].*
FROM sample_table t
GROUP BY t.ID, t.Product
Query results
You can use window function to do partition based on key and selecting required based on defining order by field.
For Example:
select * from (
select *,
rank() over (partition by product, order by DateTime Desc) as rank
from `project.dataset.table`)
where rank = 1
You can use this query to select last record of each group:
Select Top(1) * from Tablename group by ID order by DateTime Desc
This post is similar to this thread in that I have multiple observations per group. However, I want to randomly select only one of them. I am also working on Oracle 10g.
There are multiple rows per person_id in table df. I want to order each group of person_ids by dbms_random.value() and select the first observation from each group. To do so, I tried:
select
person_id, purchase_date
from
df
where
row_number() over (partition by person_id order by dbms_random.value()) = 1
The query returns:
ORA-30483: window functions are not allowed here
30483. 00000 - "window functions are not allowed here"
*Cause: Window functions are allowed only in the SELECT list of a query. And, window function cannot be an argument to another window or group function.
Use a subquery:
select person_id, purchase_date
from (select df.*,
row_number() over (partition by person_id order by dbms_random.value()) as seqnum
from df
) df
where seqnum = 1;
One option would be using WITH..AS Clause :
WITH t AS
(
SELECT df.*,
ROW_NUMBER() OVER (PARTITION BY person_id ORDER BY dbms_random.value()) AS rn
FROM df
)
SELECT person_id, purchase_date
FROM t
WHERE rn = 1
Aggregate queries (using GROUP BY and aggregate functions) are much faster than equivalent analytic functions that do the same job. So, if you have a lot of data to process, or if the data is not excessively large but you must run this query often, you may want a more efficient query that uses aggregation instead of analytic functions.
Here is one possible approach:
select person_id,
max(purchase_date) keep (dense_rank first order by dbms_random.value())
as random_purchase_date
from df
group by person_id
;
I am trying to figure out how to combine a group by with a window function
I have field as
timestamp track_name
where timestamp represents the time the track was played.
If I want to get the track that was played most each day how can I do this?
I would need a count of track_name grouped by date(timestamp), and track_name
but not sure how to do that grouped by count and then get the most for that day?
thnx!
You can certainly mix analytic functions with a GROUP BY query. In the query below, I aggregate by date and track name, but also generate a rank based on the aggregated count. For each date, the track having the highest rank is retained. Note that I use RANK rather than ROW_NUMBER, since the former can handle the possibility of two or more tracks being tied for the most number of plays on a single day.
WITH cte AS (
SELECT DATE(timestamp) AS dt, track_name,
RANK() OVER (PARTITION BY DATE(timestamp) ORDER BY COUNT(*) DESC) rnk
FROM yourTable
GROUP BY DATE(timestamp), track_name
)
SELECT dt, track_name
FROM cte
WHERE rnk = 1;
This works because analytic functions are evaluated after GROUP BY has already finished. So, the COUNT(*) is available to be used in the call to RANK().
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 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