Consider this simple table of event counts:
event_name
count
viewLoaded
20
viewUnloaded
17
buttonTapped
12
viewScrolled
12
networkSuccess
9
linkTapped
9
networkFailure
2
leapSecond
0
I would like to select the top N events by count, but with the additional requirement that if the result set includes any event with a particular count, then it should include all of the events with that count. In other words, I don’t want to break up any of the “groups” of rows that have the same count. Instead, I will potentially get more rows than I asked for.
For example, if I wanted the “top five” events in the table above, the query would actually return six rows so that both events with count 9 were included. The query for the top four would return four rows, and the query for the top three would also return four rows.
How can I accomplish this in SQLite?
You can use the RANK window function for this task. It's ranking value will be equal for the identical values, but will consider the amount of past rows when needs to assign the next ranking.
WITH cte AS (
SELECT *, RANK() OVER(ORDER BY count_ DESC) AS rn
FROM events
)
SELECT event_name, count_ FROM cte WHERE rn <= 5
Check the demo here.
One way is to use a common table expression to identify the counts corresponding to the “top five” events:
with top_five as (
select count from events order by count desc limit 5
)
select * from events where count in top_five order by count desc;
Related
I have a sample table named assets which looks like this:
id
name
block_no
1
asset1
2
2
asset2
2
3
asset3
3
There can be any number of assets in a specific block. I need a minimum of 100 rows from the table, and containing all the data from the block_no. Like, if there are 95 rows to block_no 2 and around 20 on block_no 3, I need all 20 of block_no 3 as if I am fetching data in packets based on block_no.
Is this possible and feasible?
Postgres 13 or later
There is a dead simple solution using WITH TIES in Postgres 13 or later:
SELECT *
FROM assets
WHERE block_no >= 2 -- your starting block
ORDER BY block_no
FETCH FIRST 100 ROWS WITH TIES;
This will return at least 100 rows (if enough qualify), plus all peers of the 100th row.
If your table isn't trivially small, an index on (block_no) is essential for performance.
See:
Get top row(s) with highest value, with ties
Older versions
Use the window function rank() in a subquery:
SELECT (a).*
FROM (
SELECT a, rank() OVER (ORDER BY block_no) AS rnk
FROM assets a
) sub
WHERE rnk <= 100;
Same result.
I use a little trick with the row type to strip the added rnk from the result. That's an optional addition.
See:
PostgreSQL equivalent for TOP n WITH TIES: LIMIT "with ties"?
I have a table with the following fields
ID,Content,QuestionMarks,TypeofQuestion
350, What is the symbol used to represent Bromine?,2,MCQ
758,What is the symbol used to represent Bromine? ,2,MCQ
2425,What is the symbol used to represent Bromine?,3,Essay
2080,A quadrilateral has four sides, four angles ,1,MCQ
2614,A circular cone has a curved surface area of ,2,MCQ
2520,Two triangles have sides 5 cm, 11 cm, 2 cm . ,2,MCQ
2196,Life supporting process mediated by water? ,2,Essay
I would like to get random questions where total marks is an input number.
For example if I say 25, the result should be all the random questions whose Sum(QuestionMarks) is 25(+/-1)
Is this really possible using a SQL
select content,id,questionmarks,sum(questionmarks) from quiz_question
group by content,id,questionmarks;
Expected Input 25
Expected Result (Sum of Question Marks =25)
Update:
How do I ensure I get atleast 2 Essay Type Questions (this is just an example) I would extend this for other conditions. Thank you for all the help
S-Man's cumulative sum is the right approach. For your logic, though, I think you want to get up to the first row that is 24 or more. That logic is:
where total - questionmark < 24
If you have enough questions, then you could get exactly 25 using:
with q25 as (
select *
from (select t.*,
sum(questionmark) over (order by random()) as running_questionmark
from t
) t
where running_questionmark < 25
)
select q.ID, q.Content, q.QuestionMarks, q.TypeofQuestion
from q25 q
union all
(select t.ID, t.Content, t.QuestionMarks, t.TypeofQuestion
from t cross join
(select sum(questionmark) as questionmark_25 from q25) x
where not exists (select 1 from q25 where q25.id = t.id)
order by abs(questionmark - (25 - questionmark_25))
limit 1
)
This selects questions up to 25 but not at 25. It then tries to find one more to make the total 25.
Supposing, questionmark is of type integer. Then you want to get some records in random order whose questionmark sum is not more than 25:
You can use the consecutive SUM() window function. The order is random. The consecutive SUM() adds every current value to the previous sum. So, you could filter where SUM() <= <your value>:
demo:db<>fiddle
SELECT
*
FROM (
SELECT
*,
SUM(questionmark) OVER (ORDER BY random()) as total
FROM
t
)s
WHERE total <= 25
Note:
This returns a records list with no more than 25, but as close as possible to it with an random order.
To find an exact match of your value is some sort of combinatorical problem which shouldn't be solved in a database. Especially when there's a random factor. What if your current SUM is 22 and the next randomly chosen value is 4. Would you retry maybe until infinity to randomly find a value = 3? Or are you trying to remove an already counted record with value = 1?
I have a problem with transferring an Excel formula to SQL. My excel formula is: =IF(P2<(MAX($P$2:P2));"Move";"").
The P column in excel is a sequence of numbers.
a | b
------
1
2
7
3 MOVE
4 MOVE
8
9
5 MOVE
10
You can find more example on this screenshot:
I created a cursor with a loop but I don't know how to check max from range.
For example when I iterate for fourth row, I have to check max from 1-4 row etc.
No need for a cursor and a loop. Assuming that you have a column that defines the ordering of the rows (say, id), you can use window functions:
select t.*,
case when a < max(a) over(order by id) then 'MOVE' end as b
from mytable t
One option would be using MAX() Analytic function . But in any case, you'd have an extra column such as id for ordering in order to determine the max value for the current row from the first row, since SQL statements represent unordered sets. If you have that id column with values ordered as in your sample data, then consider using
WITH t2 AS
(
SELECT MAX(a) OVER (ORDER BY id ROWS BETWEEN
UNBOUNDED PRECEDING
AND
CURRENT ROW) AS max_upto_this_row,
t.*
FROM t
)
SELECT a, CASE WHEN max_upto_this_row > a THEN 'Move' END AS b
FROM t2
ORDER BY id;
Demo
I have a table like this
and I want to return the difference between the two rows
SQL tables represent unordered sets. There is no ordering, unless a column specifies the ordering.
So, you can get the two values using MAX() and MIN(). This should do what you want:
select max(nbaction) - min(nbaction)
from t;
EDIT:
Given your actual problem, you have multiple choices. Here is one:
SELECT (SELECT nbaction
FROM analyse_page_fait
WHERE operateurdimid = 2
ORDER BY datedimid DESC
FETCH FIRST 1 ROW ONLY
) -
(SELECT nbaction
FROM analyse_page_fait
WHERE operateurdimid = 2
ORDER BY datedimid DESC
OFFSET 1
FETCH FIRST 1 ROW ONLY
) as diff
This is how my query results look like currently. How can I get the MAX() value for each unique id ?
IE,
for 5267139 is 8.
for 5267145 is 4
5267136 5
5267137 8
5267137 2
5267139 8
5267139 5
5267139 3
5267141 4
5267141 3
5267145 4
5267145 3
5267146 1
5267147 2
5267152 3
5267153 3
5267155 8
SELECT DISTINCT st.ScoreID, st.ScoreTrackingTypeID
FROM ScoreTrackingType stt
LEFT JOIN ScoreTracking st
ON stt.ScoreTrackingTypeID = st.ScoreTrackingTypeID
ORDER BY st.ScoreID, st.ScoreTrackingTypeID DESC
GROUP BY will partition your table into separate blocks based on the column(s) you specify. You can then apply an aggregate function (MAX in this case) against each of the blocks -- this behavior applies by default with the below syntax:
SELECT First_column, MAX(Second_column) AS Max_second_column
FROM Table
GROUP BY First_column
EDIT: Based on the query above, it looks like you don't really need the ScoreTrackingType table at all, but leaving it in place, you could use:
SELECT st.ScoreID, MAX(st.ScoreTrackingTypeID) AS ScoreTrackingTypeID
FROM ScoreTrackingType stt
LEFT JOIN ScoreTracking st ON stt.ScoreTrackingTypeID = st.ScoreTrackingTypeID
GROUP BY st.ScoreID
ORDER BY st.ScoreID
The GROUP BY will obviate the need for DISTINCT, MAX will give you the value you are looking for, and the ORDER BY will still apply, but since there will only be a single ScoreTrackingTypeID value for each ScoreID you can pull it out of the ordering.