Update of a table from a select query with aggregate functions.

Question

Hello All,
I have problem here:
I have 2 tables A(a1, a2, a3, a4, a4....... ) and B( a1, a2, b1, b2, b3). I need to calculate the avg(a4-a3), Max(a4-a3) and Min(a4-a3) and insert it into table B. If the foreign keys a1, a2 already exist in table B, I need to do an update of the computed values into column b1, b2 and b3 respectively, for a1, a2.
Q1. Is it possible to do this with a single query ? I would prefer not to join A with B because the table A is very large. Also columns b1, b2 and b3 are non-nullable.
Q2. Also if a4 and a3 are timestamps what is the best way to find the average? A difference of timestamps yields INTERVAL DAY TO SECOND over which the avg function doesn't seem to work. The averages, max and min in my case would be less than a day and hence all I need is to get the data in the hh:mm:ss format.
As of now I'm using :
TO_CHAR(TO_DATE(ABS(MOD(TRUNC(AVG(extract(hour FROM (last_modified_date - created_date))*3600 +
extract( minute FROM (last_modified_date - created_date))*60 +
extract( second FROM (last_modified_date - created_date)))
),86400)),'sssss'),'hh24":"mi":"ss') AS avg_time,
But this is very long drawn. Something more compact and efficient would be nice.
Thanks in advance for your inputs.
Edited by: 847764 on Mar 27, 2011 5:35 PM

Answer 1

847764 wrote:
Hi,
Thanks everyone for such fast replies. Malakshinov's example worked fine for me as far as updating the table goes. As for the timestamp computations, I'm posting additional info: Sorry, I don't understand.
If Malakshinov's example worked for updating the table, but you still have problems, does that mean you have to do something else besides update the table? If so, what?
Oracle version : Oracle Database 11g Enterprise Edition Release 11.2.0.1.0
Here are the table details :
DESC Table A
Name Null Type
ID               NOT NULL NUMBER
A1               NOT NULL VARCHAR2(4)
A2               NOT NULL VARCHAR2(40)
A3               NOT NULL VARCHAR2(40)
CREATED_DATE NOT NULL TIMESTAMP(6)
LAST_MODIFIED_DATE TIMESTAMP(6) DESCribing the tables can help clarify some things, but it's no substitute for posting CREATE TABLE and INSERT statements. With only a description of the table, nobody can re-create the problem or test their ideas. Please post CREATE TABLE and INSERT statements for both tables as they exist before the MERGE. If table b doen't contain any rows before the MERGE, then just say so, but you still need to post a CREATE TABLE statement for both tables, and INSERT statements for table a.
The objective is to compute the response times : avg (LAST_MODIFIED_DATE - CREATED_DATE), max (LAST_MODIFIED_DATE - CREATED_DATE) and min (LAST_MODIFIED_DATE - CREATED_DATE) grouped by A1 and A2 and store it in table B under AVG_T, MAX_T and MIN_T. Since AVG_T, MAX_T and MIN_T are only used for reporting purposes we have kept it as Varchar (though I think keeping it as timestamp would make more sense). I think a NUMBER would make more sense (the number of minutes, for example), or perhaps an INTERVAL DAY TO SECOND. If you stored a NUMBER, it would be easy to compute averages.
In table B the times are stored in the format : hh:mm:ss. We don't need milliseconds precision. If you don;'t need milliseconds, then you should use DATE instead of TIMESTAMP. The functions for manipulating DATEs are much better.
Hence I was calculating is as follows:
-- Avg Time
TO_CHAR(TO_DATE(ABS(MOD(TRUNC(AVG(extract(hour FROM (last_modified_date - created_date))*3600 +
extract( minute FROM (last_modified_date - created_date))*60 +
extract( second FROM (last_modified_date - created_date)))
),86400)),'sssss'),'hh24":"mi":"ss') AS avg_time,
--Max Time
extract (hour FROM MAX(last_modified_date - created_date))||':'||extract (minute FROM MAX(last_modified_date - created_date))||':'||TRUNC(extract (second FROM MAX(last_modified_date - created_date))) AS max_time,
--Min Time
extract (hour FROM MIN(last_modified_date - created_date))||':'||extract (minute FROM MIN(last_modified_date - created_date))||':'||TRUNC(extract (second FROM MIN(last_modified_date - created_date))) AS min_timeIs this something that has to be done before or after the MERGE?
Post the complete statement.
Is this part of a query? Where's the SELECT keyword?
Is this part of a DML operation? Where's the INSERT, or UPDATE, or MERGE keyword?
What are the exact results you want from this? Explain how you get those results.
Is the code above getting the right results? Are you just asking if there's a better way to get the same results?
You have to explain things very carefully. None of the people who want to help you are familiar with your application, or your needs.
I just noticed that my reply is horribly formatted - apologies! I'm just getting the hang of it.Whenever you post formatted text (such as query results) on this site, type these 6 characters:
\(small letters only, inside curly brackets) before and after each section of formatted text, to preserve spacing.