SQL get average of a list in sql select - sql

Question

We have this column in the table named "pricehistory"
1634913730;48.38,1634916509;48.38,1635162352;37.96,1635177904;49.14,1635337722;1219.98,1635340811;27.17
that is an example data.
first is the timestamp than after ; is the price at this timestamp
But i want the average price from every timestamp in a select... is that possible?
I dont find any similiar examples somewhere and my tries to select doesnt work... i am not so good with sql
so i want average of all prices behind that ; and before ,
The , split the timestamp and prices

Answer 1

Some test data :
create table test ( id int not null, pricehistory text not null );
insert into test values ( 1, '1634913730;48.38,1634916509;48.38,1635162352;37.96,1635177904;49.14,1635337722;1219.98,1635340811;27.17' );
insert into test values ( 2, '1634913731;42.42,1634916609;21.21' );
If your RDBMS has some splitting function
Then it's quite easy, just split and use AVG. Here is an example using PostgreSQL :
SELECT id, AVG(SUBSTRING(v, 12, 42)::decimal) AS average
FROM test
INNER JOIN LATERAL regexp_split_to_table(pricehistory, E',') t(v) ON TRUE
GROUP BY id;
Then you get:
id | average
----+----------------------
2 | 31.8150000000000000
1 | 238.5016666666666667
(2 rows)
Otherwise
You can use a CTE to split the values manually. This is a bit more involved. Here is an example using PostgreSQL again :
WITH RECURSIVE T AS (
SELECT id,
-- We get the last value ...
SUBSTRING(pricehistory, LENGTH(pricehistory) - STRPOS(REVERSE(pricehistory), ',') + 2) AS oneprice,
pricehistory AS remaining
FROM test
UNION ALL
-- ... as we get the other values from the recursive CTE.
SELECT id,
LEFT(remaining, STRPOS(remaining, ',') - 1),
SUBSTRING(remaining, STRPOS(remaining, ',') + 1)
FROM T
WHERE STRPOS(remaining, ',') > 0
)
SELECT id, AVG(SUBSTRING(oneprice, 12)::decimal) AS average
FROM T
GROUP BY id;
Then you get:
id | average
----+----------------------
2 | 31.8150000000000000
1 | 238.5016666666666667
(2 rows)

Answer 2

MySql >= 8.0
I used Recursive Common Table Expressions (cte) to split pricehistory string by ','. Then I split price from timestamp by ';', cast price as decimal(10,2) and group by id to get average price by id.
WITH RECURSIVE
cte AS (SELECT id,
SUBSTRING_INDEX(pricehistory, ',', 1) AS price,
CASE WHEN POSITION(',' IN pricehistory) > 0
THEN SUBSTR(pricehistory, POSITION(',' IN pricehistory) + 1)
ELSE NULL END AS rest
FROM t
UNION ALL
SELECT id,
SUBSTRING_INDEX(rest, ',', 1) AS price,
CASE WHEN POSITION(',' IN rest) > 0
THEN SUBSTR(rest, POSITION(',' IN rest) + 1)
ELSE NULL END AS rest
FROM cte
WHERE rest IS NOT NULL)
SELECT id, AVG(CAST(SUBSTR(price, POSITION(';' IN price) + 1) AS decimal(10,2))) AS price_average
FROM cte
GROUP BY id;
A similar way to do the same (using regular expressions functions):
WITH RECURSIVE
cte AS (SELECT Id, concat(pricehistory, ',') AS pricehistory FROM t),
unnest AS (SELECT id,
pricehistory,
1 AS i,
REGEXP_SUBSTR(pricehistory, ';[0-9.]*,', 1, 1) AS price
FROM cte
UNION ALL
SELECT id,
pricehistory,
i + 1,
REGEXP_SUBSTR(pricehistory, ';[0-9.]*,', 1, i + 1)
FROM unnest
WHERE REGEXP_SUBSTR(pricehistory, ';[0-9.]*,', 1, i + 1) IS NOT NULL)
SELECT id, AVG(CAST(SUBSTR(price, 2, LENGTH(price) - 2) AS decimal(10,2))) AS price_average
FROM unnest
GROUP BY id;

Answer 3

you don't write what DBMS you are using.
In MS SQL-SERVER you can write something like this.
Create a function to convert string to multiple rows, and then use that in the query.
CREATE or ALTER FUNCTION dbo.BreakStringIntoRows (#CommadelimitedString varchar(1000), #Separator VARCHAR(1))
RETURNS #Result TABLE (Column1 VARCHAR(max))
AS
BEGIN
DECLARE #IntLocation INT
WHILE (CHARINDEX(#Separator, #CommadelimitedString, 0) > 0)
BEGIN
SET #IntLocation = CHARINDEX(#Separator, #CommadelimitedString, 0)
INSERT INTO #Result (Column1)
--LTRIM and RTRIM to ensure blank spaces are removed
SELECT RTRIM(LTRIM(SUBSTRING(#CommadelimitedString, 0, #IntLocation)))
SET #CommadelimitedString = STUFF(#CommadelimitedString, 1, #IntLocation, '')
END
INSERT INTO #Result (Column1)
SELECT RTRIM(LTRIM(#CommadelimitedString))--LTRIM and RTRIM to ensure blank spaces are removed
RETURN
END
create table test1 ( id int not null, pricehistory varchar(max) not null );
insert into test1 values ( 1, '1634913730;48.38,1634916509;48.38,1635162352;37.96,1635177904;49.14,1635337722;1219.98,1635340811;27.17' );
insert into test1 values ( 2, '1634913731;42.42,1634916609;21.21' );
Select *,
(
Select avg(CAST(RTRIM(LTRIM(SUBSTRING(column1, 0, CHARINDEX(';', column1, 0)))) as decimal)) From dbo.BreakStringIntoRows(pricehistory, ',')
) as AVG
FRom test1
sample output: