Ok, I'm new using this connect by thing. But its always quite useful. I have this small problem you guys might be able to help me...
Given start month (say to_char(sysdate,'YYYYMM')) and end month (say, to_char(add_months(sysdate, 6),'YYYYMM')), want to get the list of months in between, in the same format.
Well, I want to use this into a partitions automation script. My best shot so far (pretty pitiful) yields invalid months e.g.'201034'... (and yea, I know, incredibly inefficient)
Follows the code:
SELECT id
from
(select to_char(add_months(sysdate, 6),'YYYYMM') as tn_end, to_char(sysdate,'YYYYMM') as tn_start from dual) tabla,
(select * from
(Select Level as Id from dual connect by Level <= (Select to_char(add_months(sysdate, 1),'YYYYMM')from dual)) where id > to_char(sysdate,'YYYYMM')) t
Where
t.Id between tabla.tn_start and tabla.tn_end
how do I do to make this query return only valid months? Any tips?
cheers mates,
f.
Best way might be to separate out the row generator from the date function. So generate a list from 0 to 6 and calculate months from that. If you want to pass the months in then do that in the with clause
with my_counter as (
Select Level-1 as id
from dual
connect by Level <= 7
)
select to_char(add_months(sysdate, id),'YYYYMM') from my_counter
The example below will allow you to plug in the dates you require to work out the difference.
with my_counter as (
Select Level-1 as id
from dual
connect by level <= months_between(add_months(trunc(sysdate,'MM'), 6),
trunc(sysdate,'MM')) + 1
)
select to_char(add_months(trunc(sysdate, 'MM'), id),'YYYYMM') from my_counter
For generating dates and date ranges, I strongly suggest you create a permanent calendar table with one row for each day. Even if you keep 20 years in this table it will be small ~7500 rows. Having such a table lets you attach additional (potentially non-standard) information to a date. For example your company may use a 6-week reporting period which you cannot extract using TO_CHAR / TO_DATE. Pre-compute it and store it in this table.
Oh, and Oracle 11g has automatic partition management. If you are stuck with 10g, then this article may be of interest to you? Automatic Partition Management for Oracle 10g
Try this:
with numbers as
( select level as n from dual
connect by level <= 7
)
select to_char (add_months (trunc(sysdate,'MM'), n-1), 'YYYYMM') id
from numbers;
ID
------
201012
201101
201102
201103
201104
201105
201106
Related
I have a list of 50 thousand receipt Ids (hard coded values). i want to apply these 50 thousand Ids in where condition or join operation. I have used below 'with' clause to create a temp table to collect those 50 thousand Ids. Then I used this temp table in join query for filtering.
with temp_receiptIds(receiptId)
as
(
select 'M0000001' from dual
union
select 'M0000002' from dual
union
select 'M0000003' from dual
union
select 'M0000004' from dual
..
..
...
union
select 'M0049999' from dual
union
select 'M0050000' from dual
)
select sal.receiptId, prd.product_name, prd.product_price, sal.sales_date, sal.seller_name
from product prd
join sales sal on prd.product_id=sal.product_id
join temp_receiptIds tmp on tmp.receiptId=sal.receiptId
Whenever I run the above select join query to extract data as requested by business people, it takes about 8 minutes to fetch result in the production server.
Is my above approach correct? Are there any simpler approach than this by considering best performance in the production server.
Please note, every second , the production database is used by customer. since production db is very busy, can I run this query in production db directly, will it cause slow performance in the customer using website which calls this production db in every second. Correct answers would be greatly appreciated! Thanks
Why wouldn't you store those receiptIDs into a table?
create table receiptids as
with temp_receiptIds(receiptId)
as
(
select 'M0000001' from dual
union all --> "union ALL" instead of "union"
...
)
select * from temp_receiptids;
Index it:
create index i1recid on receiptids (receiptIdD);
See how that query now behaves.
If you - for some reason - can't do that, see whether UNION ALL within the CTE does any good. For 50.000 rows, it could make a difference.
All the Oracles out here,
I have an Oracle PL/SQL procedure but very small data that can run on the query. I suspect that when the data gets large, the query might start performing back. Are there ways in which I can check for performance and take corrective measure even before the data build up? If I wait for the data buildup, it might get too late.
Do you have any general & practical suggestions for me? Searching the internet did not get me anything convincing.
Better to build yourself some test data to get an idea of how things will perform. Its easy to get started, eg
create table MY_TEST as select * from all_objects;
gives you approx 50,000 rows typically. You can scale that easily with
create table MY_TEST as select a.* from all_objects a ,
( select 1 from dual connect by level <= 10);
Now you have 500,000 rows
create table MY_TEST as select a.* from all_objects a ,
( select 1 from dual connect by level <= 10000);
Now you have 500,000,000 rows!
If you want unique values per row, then add rownum eg
create table MY_TEST as select rownum r, a.* from all_objects a ,
( select 1 from dual connect by level <= 10000);
If you want (say) 100,000 distinct values in a column then TRUNC or MOD. You can also use DBMS_RANDOM to generate random numbers, strings etc.
Also check out Morten's test data generator
https://github.com/morten-egan/testdata_ninja
for some domain specific data, and also the Oracle sample schemas on github which can also be scaled using techniques above.
https://github.com/oracle/db-sample-schemas
Everyone knows you can do SELECT SYSDATE FROM DUAL to get a single row representing today's date.
I'd like to do something similar, but it would look like:
SELECT MAGICDATE FROM DUAL
WHERE MAGICDATE = Prompted in the application software
Bit of a long story why...
I'm using a package called SAP Business Objects. It translates user queries into SQL and can get a little tricky. I would like to pull out the user prompts into separate little sub-queries, then use the results of the prompts to power my main queries.
The queries look like:
select user_id, test_centre, test_date, count(*)
from
Lots of tables
where user_id in Prompted User Id
and test_centre in Prompted test_centre
and test_date between Prompted Date 1 and Prompted Date 2
Here's one way of doing it:
SELECT TRUNC(SYSDATE) + dbms_random.value(-5000, 5000) random_date,
TRUNC(SYSDATE) + floor(dbms_random.value(-5000, 5000)) random_datetime
FROM dual;
I've provided ways to get both a random date and a random date + time. Note that I've used TRUNC(SYSDATE) as the seed date and range of 5000 days before and after. You may wish to change the seed date so that it's SYSDATE or even a fixed date, as well as to amend the date ranges as per your requirements.
Can you just do this?
select to_date([prompted_date],'someformat') from dual
The actual answer to your question is:
select #prompt(.....) from dual
But I don't think that is actually what you're looking for. Can you be more specific about what you are attempting to do?
I want to create a crosstab for LeaveCount for Employees for respective Months with iReport (JasperReports). I'm using Oracle database.
The problem is, I'm getting only the months where the measure exists, I want to display all months of the year whether the measure(Leave of Employee) exists for this month or not.
You can create a table
CREATE TABLE ALLMONTHS
(
MONTHS_MM varchar2(2)
)
;
And insert all 12 months in this table(01,02,03,04...12).
Now using this table form query as below
SELECT a.MONTHS_MM,b.leavecount
FROM ALLMONTHS a
,(SELECT to_char(leavedate,'MM') AS MONTH,leavecount..."your query")b
WHERE a.MONTHS_MM=b.MONTH(+)
That solved the issue with the answer suggested by #Pu297 . Later I got an even better method which involves no table creation and saves trouble of creating a table every time i need to run report on a new database.
select a.mnth,b.leavecount from
(
SELECT to_char(to_date(LVL,'MM'),'MM') mnth
FROM (select level lvl from dual CONNECT BY LEVEL <=12)
) a
,(SELECT to_char(leavedate,'MM') AS MONTH,leavecount..."your query")b
WHERE a.mnth=b.MONTH(+)
This is better way according to me for this issue.
Cheers!!!
I recently got some help for an oracle query and don't quite understand how it works and thus can't get it to work with my data. Is anyone able to explain the logic of what is happening in logical steps and what variables are actually taken from an existing table's columns? I am looking to select data from a table of readings (column names are: day, hour, volume) and find the average reading of volume for each hour of each day (thus GROUP BY day, hour), by going back to all readings for that hour/day combination in the past (as far back as my dataset goes) and writing out the average for it. Once that is done, it will write the results to a different table with the same column names (day, hour, volume). Except when I write it back on a per hour basis, 'volume' will be the average for that hour of the day in the past. For example, I want to find what the average was for all Wednesdays at 7pm in the past, and output the average to a new record. Assuming these 3 columns were used and in reference to the code below, I am not sure how "hours" differs to "hrs" and what the t1 variable represents. Any help is appreciated.
INSERT INTO avg_table (days, hours, avrg)
WITH xweek
AS (SELECT ds, LPAD (hrs, 2, '0') hrs
FROM ( SELECT LEVEL ds
FROM DUAL
CONNECT BY LEVEL <= 7),
( SELECT LEVEL - 1 hrs
FROM DUAL
CONNECT BY LEVEL <= 24))
SELECT t1.ds, t1.hrs, AVG (volume)
FROM xweek t1, tables t2
WHERE t1.ds = TO_CHAR (t2.day(+), 'D')
AND t1.hrs = t2.hour(+)
GROUP BY t1.ds, t1.hrs;
I'd re-write this slightly so it makes more sense (to me at least).
To break it down bit by bit, CONNECT BY is a hierarchical (recursive) query. This is a common "cheat" to generate rows. In this case 7 to represent each day of the week, numbered 1 to 7.
SELECT LEVEL ds
FROM DUAL
CONNECT BY LEVEL <= 7
The next one generates the hours 0 to 23 to represent midnight to 11pm. These are then joined together in the old style in a Cartesian or CROSS JOIN. This means that every possible combination of rows is returned, i.e. it generates every hour of every day for a single week.
The WITH clause is described in the documentation on the SELECT statement, it is commonly known as a Common Table Expression (CTE), or in Oracle the Subquery Factoring Clause. This enables you to assign a name to a sub-query and reference that single sub-query in multiple places. It can also be used to keep code clean or generate temporary tables in memory for ready access. It's not required in this case but it does help to separate the code nicely.
Lastly, the + is Oracle's old notation for outer joins. They are mostly equivalent but there are a few very small differences that are described in this question and answer.
As I said at the beginning I would re-write this to conform to the ANSI standard because I find it more readable
insert into avg_table (days, hours, avrg)
with xweek as (
select ds, lpad(hrs, 2, '0') hrs
from ( select level ds
from dual
connect by level <= 7 )
cross join ( select level - 1 hrs
from dual
connect by level <= 24 )
)
select t1.ds, t1.hrs, avg(volume)
from xweek t1
left outer join tables t2
on t1.ds = to_char(t2.day, 'd')
and t1.hrs = t2.hour
group by t1.ds, t1.hrs;
To go into slightly more detail the t1 variable represents an alias for the CTE week1, it's so you don't have to type the entire thing each time. hrs is an alias for the generated expression, as you reference it explicitly you need to call it something. HOURS is a column in your own table.
As to whether this is doing the correct thing I'm not sure, you imply you only want it for a single day rather than the entire week so only you can decide if this is correct? I also find it a little strange that you need the HOURS column in your table to be a character left-padded with 0s lpad(hrs, 2, '0'), once again, only you know if this is correct.
I would highly recommend playing about with this yourself and working out how everything goes together. You also seem to be missing some of the basics, get a text book or look around on the internet, or Stack Overflow, there's plenty of examples.