Basically I have a view which is having below query as a part of view .
SELECT site_id ch_site_id
FROM bfg_router_pi_details
WHERE last_modified_date > (SELECT MAX (last_time_stamp)
FROM saa_bfg_feed_ctl)
Now in this query bfg_router_pi_details is a view in another database and saa_bfg_feed_ctl is a table in same database from we are firing this query.
Now when This query is fired like above using inner query in where clause, it takes 2 hours to finish as it is going over the db link. however if i replace the inner query with the actual date value it takes 2 minutes. so I am trying to see if there is any way that I can define a variable in view and assign the last time stamp value to that variable and then replace that variable in the where clause of the query so that execution become s faster. hope you understood the problem in hand.
It's probably because Oracle is choosing the remote site as the driving site for the query. Try this hint to tell it to run the query from the local site:
SELECT /*+DRIVING_SITE(saa_bfg_feed_ctl) */
site_id ch_site_id
FROM bfg_router_pi_details
WHERE last_modified_date > (SELECT MAX (last_time_stamp)
FROM saa_bfg_feed_ctl)
I'm not 100% sure on this off the top of my head - if you post a plan for your query might be able to help further.
there are many ways how to do it but surely all of them require plsql programming. The most simple one is to create a package where a variable with your MAX is assigned before you make the query to the view.
so the view will look like
begin
SELECT MAX (last_time_stamp)
into your_package.your_variable
FROM saa_bfg_feed_ctl
end;
may be you need no_data_found but it's not my cup of tea
SELECT site_id ch_site_id
FROM bfg_router_pi_details
WHERE last_modified_date > your_package.your_variable
You could use user plsql context by the same way so please consider about it the original documentation - http://docs.oracle.com/cd/B28359_01/network.111/b28531/app_context.htm
Related
I'm running Apex 19.2 and I would like to create a classical or interactive report based on dynamic query.
The query I'm using is not known at design time. It depends on an page item value.
-- So I have a function that generates the SQL as follows
GetSQLQuery(:P1_MyItem);
This function may return something like
select Field1 from Table1
or
Select field1,field2 from Table1 inner join Table2 on ...
So it's not a sql query always with the same number of columns. It's completely variable.
I tried using PL/SQL function Body returning SQL Query but it seems like Apex needs to parse the query at design time.
Has anyone an idea how to solve that please ?
Cheers,
Thanks.
Enable the Use Generic Column Names option, as Koen said.
Then set Generic Column Count to the upper bound of the number of columns the query might return.
If you need dynamic column headers too, go to the region attributes and set Type (under Heading) to the appropriate value. PL/SQL Function Body is the most flexible and powerful option, but it's also the most work. Just make sure you return the correct number of headings as per the query.
I am a SQL Server guy and just started working on Netezza, one thing pops up to me is a daily query to find out the size of a table filtered out by year: 2016,2015, 2014, ...
What I am using now is something like below and it works for me, but I wonder if there is a better way to do it:
select count(1)
from table
where extract(year from datacolumn) = 2016
extract is a built-in function, applying a function on a table with size like 10 billion+ is not imaginable in SQL Server to my knowledge.
Thank you for your advice.
The only problem i see with the query is the where clause which executes a function on the 'variable' side. That effectively disables zonemaps and thus forces netezza to scan all data pages, not only those with data from that year.
Instead write something like:
select count(1)
from table
where datecolumn between '2016-01-01' and '2016-12-31'
A more generic alternative is to create a 'date dimension table' with one row per day in your tables (and a couple of years into the future)
This is an example for Postgres: https://medium.com/#duffn/creating-a-date-dimension-table-in-postgresql-af3f8e2941ac
This enables you to write code like this:
Select count(1)
From table t join d_date d on t.datecolumn=d.date_actual
Where year_actual=2016
You may not have the generate_series() function on your system, but a 'select row_number()...' can do the same trick. A download is available here: https://www.ibm.com/developerworks/community/wikis/basic/anonymous/api/wiki/76c5f285-8577-4848-b1f3-167b8225e847/page/44d502dd-5a70-4db8-b8ee-6bbffcb32f00/attachment/6cb02340-a342-42e6-8953-aa01cbb10275/media/generate_series.tgz
A couple of further notices in 'date interval' where clauses:
Those columns are the most likely candidate for a zonemaps optimization. Add a 'organize on (datecolumn)' at the bottom of your table DDL and organize your table. That will cause netezza to move around records to pages with similar dates, and the query times will be better.
Furthermore you should ensure that the 'distribute on' clause for the table results in an even distribution across data slices of the table is big. The execution of the query will never be faster than the slowest dataslice.
I hope this helps
First off, my background is in SQL Server. Using CTEs (Common Table Expressions) is a breeze and converting it to a stored procedure with variables doesn't require any changes to the structure of the SQL other than replacing entered values with variable names.
In Oracle PL/SQL however, it is a completely different matter. My CTEs work fine as straight SQL, but once I try to wrap them as PL/SQL I run into a host of issues. From my understanding, a SELECT now needs an INTO which will only hold the results of a single record. However, I am wanting the entire recordset of multiple values.
My apologies if I am missing the obvious here. I'm thinking that 99% of my problem is the paradigm shift I need to make.
Given the following example:
NOTE: I am greatly over simplifying the SQL here. I do know the below example can be done in a single SQL statement. The actual SQL is much more complex. It's the fundamentals I am looking for here.
WITH A as (SELECT * FROM EMPLOYEES WHERE DEPARTMENT = 200),
B as (SELECT * FROM A WHERE EMPLOYEE_START_DATE > date '2014-02-01'),
C as (SELECT * FROM B WHERE EMPLOYEE_TYPE = 'SALARY')
SELECT 'COUNTS' as Total,
(SELECT COUNT(*) FROM A) as 'DEPT_TOTAL',
(SELECT COUNT(*) FROM B) as 'NEW_EMPLOYEES',
(SELECT COUNT(*) FROM C) as 'NEW_SALARIED'
FROM A
WHERE rowcount = 1;
Now if I want to make this into PL/SQL with variables that are passed in or predefined at the top, it's not a simple matter of declaring the variables, popping values into them, and changing my hard-coded values into variables and running it. NOTE: I do know that I can simply change the hard-coded values to variables like :Department, :StartDate, and :Type, but again, I am oversimplifying the example.
There are three issues I am facing here that I am trying to wrap my head around:
1) What would be the best way to rewrite this using PL/SQL with declared variables? The CTEs now have to go INTO something. But then I am dealing with one row at a time as opposed to the entire table. So CTE 'A' is a single row at a time, and CTE B will only see the single row as opposed to all of the data results of A, etc. I do know that I will most likely have to use CURSORS to traverse the records, which somehow seems to over complicate this.
2) The output now has to use DBMS_OUTPUT. For multiple records, I will have to use a CURSOR with FETCH (or a FOR...LOOP). Yes?
3) Is there going to a big performance issue with this vs. straight SQL in regards to speed and resources used?
Thanks in advance and again, my apologies if I am missing something really obvious here!
First, this has nothing to do with CTEs. This behavior would be the same with a simple select * from table query. The difference is that with T-SQL, the query goes into an implicit cursor which is returned to the caller. When executing the SP from Management Studio this is convenient. The result set appears in the data window as if we had executed the query directly. But this is actually non-standard behavior. Oracle has the more standard behavior which might be stated as "the result set of any query that isn't directed into a cursor must be directed to variables." When directed into variables, then the query must return only one row.
To duplicate the behavior of T-SQL, you just have to explicitly declare and return the cursor. Then the calling code fetches from the cursor the entire result set but one row at a time. You don't get the convenience of Sql Developer or PL/SQL Developer diverting the result set to the data display window, but you can't have everything.
However, as we don't generally write SPs just to be called from the IDE, it is easier to work with Oracle's explicit cursors than SQL Server's implicit ones. Just google "oracle return ref cursor to caller" to get a whole lot of good material.
Simplest way is to wrap it into an implicit for loop
begin
for i in (select object_id, object_name
from user_objects
where rownum = 1) loop
-- Do something with the resultset
dbms_output.put_line (i.object_id || ' ' || i.object_name);
end loop;
end;
Single row query without the need to predefine the variables.
I am using Oracle SQL Developer and have a rather large query built. The query is going to be run on a monthly or quarterly basis. I was wondering if there was a way that I can do a declare statment up top and then in the code just reference these variables created. That way when someone wants to run the query they can just change the dates at the top of the code rather then have to dig through all of it. I am kind of new to Oracle SQL Developer but I know in other sql codes I built I could simply declare the variable and then set it and then in the code call the variable name. Below is an example of what I know how to do but i am having trouble in Oracle SQL Developer.
Example: I have a data base that contains the columns Business, business type(small,medium,large) number of deposits, deposit amount and deposit date. I want to build a query that outputs a quarterly summary of the number of deposits and the deposit amount and be able to change the quarter and size of the business.
Example Code from my previous SQL expereince this is an example of what I am trying to do since i can not disclose my code with the table names etc in them.
Declare #busstype,#qbegindate,#qenddate
Set #busstype = 'small'
Set #qbegindate = '01-JAN-2013'
Set #qenddate = '01-MAR-2013'
Select business,numberofdeposits,depositamount
From business_transactions
Where ('#qbegindate'<=depositdate<='#qenddate'
And businesstype = '#busstype')
Group By Business
The results would list out the businesses name and then the total deposits and total amount.
I know this code is not right but its just an example of what I am looking to do in Oracle SQL Developer. The query I have built is working fine I just find it a pain to dig through the code to change dates and criteria and was wondering how I would do something like this since i have figured out that I am not able to do this in ORACLE Sql Developer.
Here is an example with predefined variable:
set feedback off
var abc varchar2
begin
:abc := 'abc';
end;
/
select :abc as a from dual;
Output:
A
--------------------------------
abc
Common table expressions allow variables to be defined at the top of the query. For performance and style reasons this is generally not a good way to
use common table expressions. The advantage is this query can be run in any IDE and it is completely self-contained.
--Variables - change these before running.
with busstype as (select 'small' value from dual),
qbegindate as (select date '2013-01-01' value from dual),
qenddate as (select date '2013-03-01' value from dual)
--Query - do not modify code below.
select business,numberofdeposits,depositamount
from business_transactions
where depostiddate between
(select value from qbegindate)
and
(select value from qenddate)
and businesstype = (select value from busstype)
group by business, numberofdeposits,depositamount;
I have two tables in my database. Each table is having 2000 records. As I have a large number of records I would like to write the most optimal code for retrieving records. USER_DETAILS table is:
+---------+-----------+-----------+
| user_id | user_name | join_date |
+---------+-----------+-----------+
The second table which is refering USER_DETAILS table is:
+---------+-----------+-----------+
| user_id | fav_color | fav_dish |
+---------+-----------+-----------+
I have two approaches first one:
SELECT UD.*,FAV.FAV_COLOR, FAV.FAV_DISH FROM USER_DETAILS UD, FAV_DETAILS FAV
WHERE UD.USER_ID = FAV.USER_ID;
Second approach is writing a PL/SQL procedure which is:
DECLARE
CURSOR C1(X NUMBER) IS SELECT * FROM USER_DETAILS WHERE USER_ID = X;
CURSOR C2 IS SELECT * FROM USER_FAV;
Y NUMBER := &USER_ID;
BEGIN
FOR C IN C1(Y)
LOOP
DBMS_OUTPUT.PUT_LINE('USER DETAILS');
DBMS_OUTPUT.PUT_LINE('----------------');
FOR D IN C2
LOOP
IF C.DEPTNO = D.DEPTNO THEN
DBMS_OUTPUT.PUT_LINE(RPAD(C.USER_ID,10)||RPAD(C.USER_NAME,10)||RPAD(D.FAV_COLOR,10));
END IF;
END LOOP;
END LOOP;
END;
Which code will give better performance and why? I want to get the complete details of a user.
If I am using cursor will I get all the records form the server to the SGA? I will use this database in a JSP page which will be accessed by mobile devices only.
As internet in mobile device is very slow of my target users (around 10KB) hence I am concerned about bandwidth. In my point of view I find that performing a join will do a Cartesian product and check for matching result which will take one condition out of 1000*1000 conditions where as the checking conditions in PL/SQL block is only 1000 + 1000. It reduces the number of conditions. But as per my knowledge cursor will create a shadow page in client memory and it will create the table. This means it will fetch all the data form the server and store in client. Am I correct at this point?
You can read here Tom Kyte's mantra:
You should do it in a single SQL statement if at all possible.
If you cannot do it in a single SQL Statement, then do it in PL/SQL.
If you cannot do it in PL/SQL, try a Java Stored Procedure.
If you cannot do it in Java, do it in a C external procedure.
If you cannot do it in a C external routine, you might want to seriously think about why it is you need to do it…
Basically by using a plsql stored procedure you move from sql engine to plsql engine back and forward. More then that, if you have the right indexes and you build your query right, the sql optimizer will probably make things faster than you.
Here is another good AskTom post
Generally using a single select statement will have better performance
by a single select you will hit RDBMS Sql engine once and RDMS will use internal procedures (indexes, cashed queries ...) boosting performance.
In programming way (ignoring internal RDMS functionality)
in the first query you are doing a search with order of efficiency O(n)
in second plsql statement, by using nested loops you are doing a search with order of efficiency O(n^2)
search order of efficiency
Use cursor when you want a pointer on each row of your rsult in order to perform further actions. If you just need a select statement, just do a select statment. Cursor is will be an overkill. Keep it simple.