Find difference between max and second max, grouped by columns in MySql (8.0.13), without using the order by...
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I have a table with the columns ID, ad_id, amount_time, which shows the ID of users, the ad that they saw, and how much time they seen it. Here is an example of the data:
table name: ads
ID | ad_id | amount_time
1 2 600
1 3 300
3 1 400
1 3 100
1 1 700
We want the result to show the difference between max and 2nd max of amount_time, grouped by ID and ad_id
So the result is
ID |ad_id | diff_amount_time
1 3 200
I can get the max and second_max of the total table by executing:
select
(SELECT MAX(amount_time) FROM ads) maxtime,
(SELECT MAX(amount_time) FROM ads
WHERE amount_time NOT IN (SELECT MAX(amount_time) FROM ads )) as
second_max_time
However, I am having trouble incorporating the group by clause in order to get my result. I know there's a way to incorporate order by and limit 2 to get the max and and second max, but this is computationally expensive and want to know if there is another solution without ordering the amount_time column.
mysql group-by max
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
|
show 4 more comments
I have a table with the columns ID, ad_id, amount_time, which shows the ID of users, the ad that they saw, and how much time they seen it. Here is an example of the data:
table name: ads
ID | ad_id | amount_time
1 2 600
1 3 300
3 1 400
1 3 100
1 1 700
We want the result to show the difference between max and 2nd max of amount_time, grouped by ID and ad_id
So the result is
ID |ad_id | diff_amount_time
1 3 200
I can get the max and second_max of the total table by executing:
select
(SELECT MAX(amount_time) FROM ads) maxtime,
(SELECT MAX(amount_time) FROM ads
WHERE amount_time NOT IN (SELECT MAX(amount_time) FROM ads )) as
second_max_time
However, I am having trouble incorporating the group by clause in order to get my result. I know there's a way to incorporate order by and limit 2 to get the max and and second max, but this is computationally expensive and want to know if there is another solution without ordering the amount_time column.
mysql group-by max
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
1
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
How do you get200?
– Eric
Nov 16 '18 at 19:29
1
@KevinSunMAX()function will also do a full table scan if there is no indexing. Same thing is applicable forORDER BY. MySQL has significantly optimized usage ofORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
1
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyzeEXPLAINstatement results for the same.
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53
|
show 4 more comments
I have a table with the columns ID, ad_id, amount_time, which shows the ID of users, the ad that they saw, and how much time they seen it. Here is an example of the data:
table name: ads
ID | ad_id | amount_time
1 2 600
1 3 300
3 1 400
1 3 100
1 1 700
We want the result to show the difference between max and 2nd max of amount_time, grouped by ID and ad_id
So the result is
ID |ad_id | diff_amount_time
1 3 200
I can get the max and second_max of the total table by executing:
select
(SELECT MAX(amount_time) FROM ads) maxtime,
(SELECT MAX(amount_time) FROM ads
WHERE amount_time NOT IN (SELECT MAX(amount_time) FROM ads )) as
second_max_time
However, I am having trouble incorporating the group by clause in order to get my result. I know there's a way to incorporate order by and limit 2 to get the max and and second max, but this is computationally expensive and want to know if there is another solution without ordering the amount_time column.
mysql group-by max
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
I have a table with the columns ID, ad_id, amount_time, which shows the ID of users, the ad that they saw, and how much time they seen it. Here is an example of the data:
table name: ads
ID | ad_id | amount_time
1 2 600
1 3 300
3 1 400
1 3 100
1 1 700
We want the result to show the difference between max and 2nd max of amount_time, grouped by ID and ad_id
So the result is
ID |ad_id | diff_amount_time
1 3 200
I can get the max and second_max of the total table by executing:
select
(SELECT MAX(amount_time) FROM ads) maxtime,
(SELECT MAX(amount_time) FROM ads
WHERE amount_time NOT IN (SELECT MAX(amount_time) FROM ads )) as
second_max_time
However, I am having trouble incorporating the group by clause in order to get my result. I know there's a way to incorporate order by and limit 2 to get the max and and second max, but this is computationally expensive and want to know if there is another solution without ordering the amount_time column.
mysql group-by max
mysql group-by max
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
edited Nov 16 '18 at 19:26
Kevin Sun
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
asked Nov 16 '18 at 18:39
Kevin SunKevin Sun
12518
12518
1
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
How do you get200?
– Eric
Nov 16 '18 at 19:29
1
@KevinSunMAX()function will also do a full table scan if there is no indexing. Same thing is applicable forORDER BY. MySQL has significantly optimized usage ofORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
1
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyzeEXPLAINstatement results for the same.
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53
|
show 4 more comments
1
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
How do you get200?
– Eric
Nov 16 '18 at 19:29
1
@KevinSunMAX()function will also do a full table scan if there is no indexing. Same thing is applicable forORDER BY. MySQL has significantly optimized usage ofORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
1
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyzeEXPLAINstatement results for the same.
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53
1
1
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
How do you get
200?– Eric
Nov 16 '18 at 19:29
How do you get
200?– Eric
Nov 16 '18 at 19:29
1
1
@KevinSun
MAX() function will also do a full table scan if there is no indexing. Same thing is applicable for ORDER BY. MySQL has significantly optimized usage of ORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
@KevinSun
MAX() function will also do a full table scan if there is no indexing. Same thing is applicable for ORDER BY. MySQL has significantly optimized usage of ORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
1
1
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyze
EXPLAIN statement results for the same.– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyze
EXPLAIN statement results for the same.– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53
|
show 4 more comments
1 Answer
1
active
oldest
votes
In MySQL 8.0.2+, simplest and possibly most performant way would be to use Window Functions.
We will use Row_Number() function, which will determine the row number values within a combination of ID and ad_id. Row number will be based on descending order amount_time value. So the highest amount_time value will have row number of 1, and the second highest would have row number of 2.
Now, we will use this result-set as a Derived Table, and aggregate (GROUP BY) on ID and ad_id. We can use conditional CASE .. WHEN expressions, to determine the difference between the highest and second highest value within every group.
SELECT
dt.ID,
dt.ad_id,
(MAX(CASE WHEN dt.row_no = 1 THEN dt.amount_time END) -
MAX(CASE WHEN dt.row_no = 2 THEN dt.amount_time END)) AS diff_amount_time
FROM
(
SELECT
ID,
ad_id,
amount_time,
ROW_NUMBER() OVER (PARTITION BY CONCAT(ID, '-', ad_id)
ORDER BY amount_desc) AS row_no
FROM ads
) AS dt
GROUP BY dt.ID, dt.ad_id
-- to remove cases where there is no second highest
-- when there is no second highest amount, then the difference will be null
-- because 5 - null = null
HAVING diff_amount_time IS NOT NULL
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
add a comment |
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active
oldest
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oldest
votes
active
oldest
votes
In MySQL 8.0.2+, simplest and possibly most performant way would be to use Window Functions.
We will use Row_Number() function, which will determine the row number values within a combination of ID and ad_id. Row number will be based on descending order amount_time value. So the highest amount_time value will have row number of 1, and the second highest would have row number of 2.
Now, we will use this result-set as a Derived Table, and aggregate (GROUP BY) on ID and ad_id. We can use conditional CASE .. WHEN expressions, to determine the difference between the highest and second highest value within every group.
SELECT
dt.ID,
dt.ad_id,
(MAX(CASE WHEN dt.row_no = 1 THEN dt.amount_time END) -
MAX(CASE WHEN dt.row_no = 2 THEN dt.amount_time END)) AS diff_amount_time
FROM
(
SELECT
ID,
ad_id,
amount_time,
ROW_NUMBER() OVER (PARTITION BY CONCAT(ID, '-', ad_id)
ORDER BY amount_desc) AS row_no
FROM ads
) AS dt
GROUP BY dt.ID, dt.ad_id
-- to remove cases where there is no second highest
-- when there is no second highest amount, then the difference will be null
-- because 5 - null = null
HAVING diff_amount_time IS NOT NULL
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
add a comment |
In MySQL 8.0.2+, simplest and possibly most performant way would be to use Window Functions.
We will use Row_Number() function, which will determine the row number values within a combination of ID and ad_id. Row number will be based on descending order amount_time value. So the highest amount_time value will have row number of 1, and the second highest would have row number of 2.
Now, we will use this result-set as a Derived Table, and aggregate (GROUP BY) on ID and ad_id. We can use conditional CASE .. WHEN expressions, to determine the difference between the highest and second highest value within every group.
SELECT
dt.ID,
dt.ad_id,
(MAX(CASE WHEN dt.row_no = 1 THEN dt.amount_time END) -
MAX(CASE WHEN dt.row_no = 2 THEN dt.amount_time END)) AS diff_amount_time
FROM
(
SELECT
ID,
ad_id,
amount_time,
ROW_NUMBER() OVER (PARTITION BY CONCAT(ID, '-', ad_id)
ORDER BY amount_desc) AS row_no
FROM ads
) AS dt
GROUP BY dt.ID, dt.ad_id
-- to remove cases where there is no second highest
-- when there is no second highest amount, then the difference will be null
-- because 5 - null = null
HAVING diff_amount_time IS NOT NULL
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
add a comment |
In MySQL 8.0.2+, simplest and possibly most performant way would be to use Window Functions.
We will use Row_Number() function, which will determine the row number values within a combination of ID and ad_id. Row number will be based on descending order amount_time value. So the highest amount_time value will have row number of 1, and the second highest would have row number of 2.
Now, we will use this result-set as a Derived Table, and aggregate (GROUP BY) on ID and ad_id. We can use conditional CASE .. WHEN expressions, to determine the difference between the highest and second highest value within every group.
SELECT
dt.ID,
dt.ad_id,
(MAX(CASE WHEN dt.row_no = 1 THEN dt.amount_time END) -
MAX(CASE WHEN dt.row_no = 2 THEN dt.amount_time END)) AS diff_amount_time
FROM
(
SELECT
ID,
ad_id,
amount_time,
ROW_NUMBER() OVER (PARTITION BY CONCAT(ID, '-', ad_id)
ORDER BY amount_desc) AS row_no
FROM ads
) AS dt
GROUP BY dt.ID, dt.ad_id
-- to remove cases where there is no second highest
-- when there is no second highest amount, then the difference will be null
-- because 5 - null = null
HAVING diff_amount_time IS NOT NULL
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
In MySQL 8.0.2+, simplest and possibly most performant way would be to use Window Functions.
We will use Row_Number() function, which will determine the row number values within a combination of ID and ad_id. Row number will be based on descending order amount_time value. So the highest amount_time value will have row number of 1, and the second highest would have row number of 2.
Now, we will use this result-set as a Derived Table, and aggregate (GROUP BY) on ID and ad_id. We can use conditional CASE .. WHEN expressions, to determine the difference between the highest and second highest value within every group.
SELECT
dt.ID,
dt.ad_id,
(MAX(CASE WHEN dt.row_no = 1 THEN dt.amount_time END) -
MAX(CASE WHEN dt.row_no = 2 THEN dt.amount_time END)) AS diff_amount_time
FROM
(
SELECT
ID,
ad_id,
amount_time,
ROW_NUMBER() OVER (PARTITION BY CONCAT(ID, '-', ad_id)
ORDER BY amount_desc) AS row_no
FROM ads
) AS dt
GROUP BY dt.ID, dt.ad_id
-- to remove cases where there is no second highest
-- when there is no second highest amount, then the difference will be null
-- because 5 - null = null
HAVING diff_amount_time IS NOT NULL
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
edited Nov 16 '18 at 19:49
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
answered Nov 16 '18 at 19:37
Chowkidar Madhur BhaiyaChowkidar Madhur Bhaiya
19.8k62336
19.8k62336
add a comment |
add a comment |
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1
What is your MySQL server version ?
– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:24
Just edited it in the title. Thanks for the reminder.
– Kevin Sun
Nov 16 '18 at 19:26
How do you get
200?– Eric
Nov 16 '18 at 19:29
1
@KevinSun
MAX()function will also do a full table scan if there is no indexing. Same thing is applicable forORDER BY. MySQL has significantly optimized usage ofORDER BY. Would recommend you to read this article: dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:52
1
Infact, problem with your approach would be usage of multiple subqueries, and multiple MAX() function calls. This will be much more inefficient. You can analyze
EXPLAINstatement results for the same.– Chowkidar Madhur Bhaiya
Nov 16 '18 at 19:53