I am looking for the dynamic result set to be return from procedure as we have in SQL Server.
In the earlier version of Postgres there was not procedure till version 10, but now in 11 we do have procedures.
I tried with functions in the postgresql but we need to provide the return type for the functions. But I am looking for the result which is dynamic, I mean to say sometimes the results comes from different table with different columns list based on the conditions check.
As I saw some of the examples of procedures from EDB, Unable to find an example for retrieving data.
Related
I tried to search for it in the official docs but no luck.
Can Postgres 13 stored procedures return multiple result sets similar to SQL Server?
If you mean to return a result set by executing a plain query - no, such syntax is not supported in PL/pgSQL.
If you mean to return a result set by using a cursor - yes, PostgreSQL stored procedures can return cursors too.
You can define multiple cursor output parameters: https://www.postgresql.org/docs/13/plpgsql-cursors.html
i have a DB2 data source and an Oracle 12c target.
The Oracle has a DB link to the DB2 defined which is working in general.
Now i have a huge table in the DB2 which has a timestamp column (lets call it ROW_CHANGED) for row changes. I want to retrieve rows which have changed after a particular time.
Running
SELECT * FROM lib.tbl WHERE ROW_CHANGED >'2016-08-01 10:00:00'
on the DB2 returns exactly 1 row after ca. 90 secs which is fine.
Now i try the same query from the Oracle via the db link:
SELECT * FROM lib.tbl#dblink_name WHERE ROW_CHANGED >TO_TIMESTAMP('2016-08-01 10:00:00')
This runs for hours and ends up in a timeout.
I read some Oracle docs and found distributed query optimization tips but most of them refer to joining a local to a remote table which is not my case.
In my desperation, i have tried the DRIVING_SITE hint, without effect.
Now i wonder when the WHERE part of the query will be evaluated. Since i have to use Oracle syntax and not DB2 syntax for the query, is it possible the Oracle will try to first copy the full table and apply the where clause afterwards? I did some research but did not find anything which would help me in this direction.
The ROW_CHANGED is a hidden column in the DB2, if that matters.
Thx for any hint in advance.
Update
Thanks#all for help. I'll share what did the trick for me.
First of all i have used TO_TIMESTAMP since the DB2 column is also Timestamp (not date) and i had expected to circumvent implicit conversions by this.
Without the explicit conversion i ran into ORA-28534: Heterogeneous Services preprocessing error and i have no hope of touching the DB config within reasonable time.
The explain plan btw did not bring much. It showed a FULL hint and no conversion on the predicates. Indeed it showed the ROW_CHANGED column as Date, i wonder why.
I have tried Justins suggestion to use a bind variable, however i got ORA-28534 again. Next thing i did was to wrap it into a pl/sql block (will run in a SP anyway later).
declare
v_tmstmp TIMESTAMP := 01.08.16 10:00:00;
begin
INSERT INTO ORAUSER.TMP_TBL (SRC_PK,ROW_CHANGED)
SELECT SRC_PK,ROW_CHANGED
FROM lib.tbl#dblink_name
WHERE ROW_CHANGED > v_tmstmp;
end;
This was executing in the same time as in DB2 itself. The date format is DD.MM.YY here since it is the default unfortunately.
When changing the variable assignment to
v_tmstmp TIMESTAMP := TO_TIMESTAMP('01.08.16 10:00:00','DD.MM.YY HH24:MI:SS');
I got the same problem as before.
Meanwhile the DB2 operators have created an index in the ROW_CHANGED column which i requested earlier that day. This has solved the problem in general it seems. Even my original query finishes in no time now.
If you are actually using an Oracle-specific conversion function like to_timestamp, that forces the predicate to be evaluated on the Oracle side. Oracle isn't going to know how to convert a built-in function like to_timestamp into an exactly equivalent function call in DB2.
If you used a bind variable, that would be more likely to get evaluated on the DB2 side. But that may be complicated by the data type mapping between different databases-- there may not be a perfect mapping between one engine's date and another engine's timestamp data type. If this was a numeric column, a bind variable would be almost certain to get pushed. In this case, it probably involves playing around a bit to figure out exactly what data type to use for your variable that works for your framework, Oracle, and DB2.
If using a bind variable doesn't work, you can force the predicate to be evaluated on the remote server using the dbms_hs_passthrough package. That lets you send a query verbatim to the remote server which allows you to do things like use functions defined in your DB2 database. That's a bit of overkill in this situation, hopefully, but it's nice to have the hammer as your backup if the simpler solution doesn't work quickly enough.
Сan you help me to convert this Oracle rule to T-SQL.
SELECT CAST(SYS_CONTEXT('CLIENTCONTEXT', 'AccessSubject') AS NVARCHAR2(255)) AS AccessSubjectCode FROM DUAL
I would like to know how this will be in T-SQL : SYS_CONTEXT()
The SYS_CONTEXT('CLIENTCONTEXT', 'AccessSubject') call returns a value configured by the client application. See https://docs.oracle.com/cd/B28359_01/network.111/b28531/app_context.htm#DBSEG98209 for details.
The most similar feature in SQL Server is the CONTEXT_INFO() function. See https://msdn.microsoft.com/en-us/library/ms180125.aspx. However, in SQL Server the context can store just a single value, of maximum 128 bytes (as opposed to Oracle, where there are multiple contexts and you can store multiple named values in each context).
I have a stored procedure in my project under sql/my_prod.sql
there I have my function delete_entity
In my entity
#NamedNativeQuery(name = "delete_entity_prod",
query = "{call /sql/delete_entity(:lineId)}",
and I call it
Query query = entityManager.createNamedQuery("delete_entity_prod")
setParameter("lineId",lineId);
I followed this example: http://objectopia.com/2009/06/26/calling-stored-procedures-in-jpa/
but it does not execute the delete and it does not send any error.
I haven't found clear information about this, am I missing something? Maybe I need to load the my_prod.sql first? But how?
JPA 2.1 standardized stored procedure support if you are able to use it, with examples here http://en.wikibooks.org/wiki/Java_Persistence/Advanced_Topics#Stored_Procedures
This is actually they way you create a query.
Query query = entityManager.createNamedQuery("delete_entity_prod")
setParameter("lineId",lineId);
To call it you must execute:
query.executeUpdate();
Of course, the DB must already contain the procedure. So if you have it defined in your SQL file, have a look at Executing SQL Statements from a Text File(this is for MySQL but other database systems use a similar approach to execute scripts)
There is no error shown because query is not executed at any point - just instance of Query is created. Query can be executed by calling executeUpdate:
query.executeUpdate();
Then next problem will arise: Writing some stored procedures to file is not enough - procedures live in database, not in files. So next thing to do is to check that there is correct script to create stored procedure in hands (maybe that is currently content of sql/my_prod.sql) and then use that to create procedure via database client.
All JPA implementations do not support calling stored procedures, but I assume Hibernate is used under the hood, because that is also used in linked tutorial.
It can be the case that current
{call /sql/delete_entity(:lineId)}
is right syntax for calling stored procedure in your database. It looks rather suspicious because of /sql/. If it turns out that this is incorrect syntax, then:
Consult manual for correct syntax
Test via client
Use that as a value of query attribute in NamedNativeQuery annotation.
All that with combination MySQL+Hibernate is explained for example here.
I have a generic code that is used to retrieve DDL information from a Firebird database (FB2.1). It generates SQL code like
SELECT * FROM MyTable where 'c' <> 'c'
I cannot change this code. Actually, if that matters, it is inside Report Builder 10.
The fact is that some tables from my database are becoming a litle too populated (>1M records) and that query is starting to take too long to execute.
If I try to execute
SELECT * FROM MyTable where SomeIndexedField = SomeImpossibleValue
it will obviously use that index and run very quickly.
Well, it wouldn´t be that hard to the database find out that that is an impossible matcher and make some sort of optimization and avoid testing it against each row.
Is there any way to make my firebird database to optimize that search?
As the filter condition is a negative proposition (and also doesn't refer a column to search, but only a value to compare to another value), Firebird need to do a full table scan (without use any index) to confirm that aren't any record that meet your criteria.
If you can't change you need to wait for the upcoming 3.0 version, that will implement the Boolean data type, and therefore should start to evaluate "constant" fake comparisons in advance (maybe the client library will do this evaluation before send the statement to the server?).