It can't calculate count(*) in a query onto DB2 database - db2

Question

I want to do a count(*) of the number of a rows fom a DB2 database.
The basic query is the following:
select
SUBSTR("Request_Detail",LOCATE('/',"Request_Detail")+1,LOCATE('/',"Request_Detail",LOCATE('/',"Request_Detail")+1)-LOCATE('/',"Request_Detail"))
from "Request_Analisys"
WHERE
"Sample_Date_and_Time">=1200323230000000 and "Sample_Date_and_Time"<1200332300000000
and "Request_Detail" <> '[Summary]'
and "Request_Detail" not like 'WS:%'
Now I'd like to do a count(*) of the resulting rows, but if I do a query like this:
select
count(*),
SUBSTR("Request_Detail",LOCATE('/',"Request_Detail")+1,LOCATE('/',"Request_Detail",LOCATE('/',"Request_Detail")+1)-LOCATE('/',"Request_Detail"))
from "Request_Analisys"
WHERE
"Sample_Date_and_Time">=1200323230000000 and "Sample_Date_and_Time"<1200332300000000
and "Request_Detail" <> '[Summary]'
and "Request_Detail" not like 'WS:%'
It gives the error:
18:51:58 FAILED [SELECT - 0 rows, 0.032 secs] 1) [Code: -119, SQL State: 42803] An expression starting with "Request_Detail" specified in a SELECT clause, HAVING clause, or ORDER BY clause is not specified in the GROUP BY clause or it is in a SELECT clause, HAVING clause, or ORDER BY clause with a column function and no GROUP BY clause is specified.. SQLCODE=-119, SQLSTATE=42803, DRIVER=4.22.29
2) [Code: -727, SQL State: 56098] An error occurred during implicit system action type "2". Information returned for the error includes SQLCODE "-119", SQLSTATE "42803" and message tokens "Request_Detail".. SQLCODE=-727, SQLSTATE=56098, DRIVER=4.22.29
How could I do to get the count of the rows?

Answer 1

Which Request_Detail line's substr would you think it shows after the count?
If you count the lines, the result set will be a single line, and using any columns in it makes no sense.
If you want multiple lines, with a count for each found substr, you need to GROUP BY this substr.

Answer 2

This may work...
select
count(
SUBSTR("Request_Detail"
,LOCATE('/',"Request_Detail")+1
,LOCATE('/',"Request_Detail",LOCATE('/',"Request_Detail")+1)
-LOCATE('/',"Request_Detail")))
)
from "Request_Analisys"
WHERE
"Sample_Date_and_Time">=1200323230000000 and "Sample_Date_and_Time"<1200332300000000
and "Request_Detail" <> '[Summary]'
and "Request_Detail" not like 'WS:%'
But if not this should..
with cte as (
select
SUBSTR("Request_Detail"
,LOCATE('/',"Request_Detail")+1
,LOCATE('/',"Request_Detail",LOCATE('/',"Request_Detail")+1)
-LOCATE('/',"Request_Detail"))) as mydetail
from "Request_Analisys"
WHERE
"Sample_Date_and_Time">=1200323230000000 and "Sample_Date_and_Time"<1200332300000000
and "Request_Detail" <> '[Summary]'
and "Request_Detail" not like 'WS:%'
)
select count(*) from cte

Answer 3

I suggest you use REGEXP_EXTRACT to pick what you want out of your "Request_Detail" column. This is more flexable than using SUBSTR and LOCATE, and will avoid the statement was not executed because a numeric argument of a scalar function is out of range.. error
e.g
select
REGEXP_EXTRACT("Request_Detail",'.*/(.+/)',1,1,'',1)
, SUBSTR("Request_Detail",LOCATE('/',"Request_Detail")+1,LOCATE('/',"Request_Detail",LOCATE('/',"Request_Detail")+1)-LOCATE('/',"Request_Detail"))
FROM TABLE(VALUES('aaaa/bbbb/ccc')) AS T("Request_Detail")
returns
1 |2
------|-----
bbbb/ |bbbb/
so, you could then do this
SELECT
COUNT(*)
, REGEXP_EXTRACT("Request_Detail",'.*/(.+/)',1,1,'',1)
FROM
"Request_Analisys"
GROUP BY
REGEXP_EXTRACT("Request_Detail",'.*/(.+/)',1,1,'',1)
for example