This question already has answers here:
Does Oracle have an equivalent of SQL Server's table variables?
(4 answers)
Closed 8 years ago.
I've recently started a new position as a developer and I'm having a bit of trouble with PL/SQL. I've used MS SQL for a number of years but I'm finding PL/SQL a bit trickier.
One of the things I used to do when writing functions and stored procedures in MS SQL was to put reoccuring result sets into a table variable so I wouldn't have to requery them throughout my procedure.
Something like this:
declare #badPeople table(recordPointer int)
insert into #badPeople
select BP_Record_Pointer
from People
where BP_Bad = 1
I'm looking at doing something similar in PL/SQL but I'm not quite sure how to get started. Any ideas if this is even possible?
declare
type t_number is table of number;
v_numbers t_number;
begin
select BP_Record_Pointer
bulk collect into v_numbers
from People
where BP_Bad = 1;
end;
This will create a nested table containing the values from your table. It's important to note that the table will go out-of-scope at the end of the anonymous block, so anything you want to do with it needs to be done inside that block.
In Oracle unlike MS SQL cursors are not considered the devil and something to avoid. So typically in Oracle you will make use of cursors much more often than you would in MS SQL. Of course if you can do it with only SQL and no cursor that is best, but don't be afraid to test and use cursors in Oracle. Get a good book on PL/SQL, this is a good one http://www.amazon.com/Oracle-PL-SQL-Programming-4th/dp/0596009771. The post by Gratzy is another option you can use. So get a good book that you can use to figure out when to use what. PL/SQL is a very rich environment compared to T-SQL. While it has more of a learning curve once you get over the initial curve it's a really easy and power full language. And on top of that it's a lot of fun.
Related
I occasionally encounter examples where SELECT...INTO...FROM DUAL is used to call a function - e.g.:
SELECT some_function INTO a_variable FROM DUAL;
is used, instead of
a_variable := some_function;
My take on this is that it's not good practice because A) it makes it unclear that a function is being invoked, and B) it's inefficient in that it forces a transition from the PL/SQL engine to the SQL engine (perhaps less of an issue today).
Can anyone explain why this might have been done, e.g. was this necessary in early PL/SQL coding in order to invoke a function? The code I'm looking at may date from as early as Oracle 8.
Any insights appreciated.
This practice dates from before PLSQL and Oracle 7. As already mentioned assignment was possible (and of course Best Practice) in Oracle7.
Before Oracle 7 there were two widely used Tools that needed the use of Select ... into var from dual;
On the one hand there used to be an Oracle Tool called RPT, some kind of report generator. RPT could be used to create batch processes. It had two kinds of macros, that could be combined to achieve what we use PLSQL for today. My first Oracle job involved debugging PLSQL that was generated by a program that took RPT batches and converted them automatically to PLSQL. I threw away my only RPT handbook sometime shortly after 2000.
On the other hand there was Oracle Forms 2.x and its Menu component. Context switching in Oracle Menu was often done with a Select ... from dual; I still remember how proud I was when I discovered that an untractable Bug was caused by a total of 6 records in table Dual.
I am sorry to say that I can not proof any of this, but it is the time of year to think back to the old times and really fun to have the answer.
I have a PL/SQL package where i want to declare a select-statment which are used by different other Packages. So i see to ways. First way i define a cursor which can be called from other packages and store the select. Second way would be a procedure which stored the select.
Can someone tell me the advantages and disadvantages of each way? My Prof. say Cursor are old and statefull and noone use this today. My Chef tell me Cursor is faster to iterate and you can make Types of it.
Can someone tell me what's the best practice here?
For example:
CURSOR crs_active_customer IS
SELECT * FROM customer where status = 'active'
OR
PROCEDURE prc_getActiveCustomer IS
BEGIN
SELECT * FROM customer where status = 'active';
END prc_getActiveCustomer;
What is better way to store select-statements.
I would write a function that returns a new cursor instance every time you call it. A cursor variable in a package is actually a GLOBAL variable: you can have only one procedure at a time using it. This is probably the problem your professor is referring to.
Having a global cursor means that you will run into "cursor already open" errors if you write a a procedure that, while scanning the results of such cursor calls another function that internally needs to use the same cursor.
PL/SQL 101 to the rescue ! From Working with Cursors:
The central purpose of the Oracle PL/SQL language is to make it as easy and efficient as possible to query and change the contents of tables in a database. You must, of course, use the SQL language to access tables, and each time you do so, you use a cursor to get the job done.
So every time you have SQL in PL/SQL there will be a cursor. The next question is what kinds of cursors there is and when to use them. The above mentioned article touches also this topic.
You can also read the fine manual: Cursors
A cursor is a pointer to a private SQL area that stores information about processing a specific SELECT or DML statement.
And then carry on reading about implicit and explicit cursors.
Next find a better professor.
This question already has an answer here:
Alternate method to global temp tables for Oracle Stored Procedure
(1 answer)
Closed 8 years ago.
I need a way to temporarily store and use multiple values returned from an Oracle query. In SQL Server, I stored my values in a temp table, did my work, then dropped the table. I'm discovering the Oracle equivalent isn't as clear cut.
Here's a SQL Server example of what I'm trying to do:
select id into #temp from SomeTable where SomeColumn = 'Some Value'
:
(do whatever I need to do with #temp data)
:
drop table #temp
I can code my way around SQL Server pretty well, but am almost clueless when it comes to Oracle syntax. I've been reading various Oracle references, and they haven't been very helpful. I did read that Oracle temp tables work differently than SQL, and are often not recommended.
I'm looking into the temp table route, but if there's a better way to do this that doesn't use temp tables, I'm all ears. Anyone know a better way to do this in Oracle?
Thanks in advance.
As with many things, that depends. It depends on how much data you'll be retrieving and how you want to use it. If you don't have too much data to work with ("too much" meaning, oh, say, more than a couple thousand rows) and you want to manipulate the data procedurally, i.e. in a PL/SQL procedure or script, AND you don't want to access it using DML, i.e. you don't want to say something like SELECT * FROM your_temp_data... than loading the data into a PL/SQL collection, as #EgorSkriptunoff mentions above, might be a workable solution.
However, if the temp data is large (more than a couple thousand rows) and/or you need to be able to do something like SELECT * FROM your_temp_data... then your best bet it to use Oracle's Global Temp Tables. A GTT is a table which is used to hold data which should only last as long as either a single transaction or a complete session (i.e. as long as you're attached to the database). Documentation here and here, and another write-up on them here.
Share and enjoy.
I just discovered Oracle's ANYDATA and ANYTYPE and thought it would be useful to generic-ify some very repetitive code I have. I tried a very simple code sample that looks like this:
declare
--simple test query
cursor myCurs is
select sysdate from dual;
type t_arr is table of myCurs%rowtype;
v_arr t_arr;
v_anydata ANYDATA;
begin
open myCurs;
fetch myCurs bulk collect into v_arr;
close myCurs;
dbms_output.put_line(v_arr.count || ' records');
v_anydata := ANYDATA.convertCollection(v_arr);
dbms_output.put_line(anydata.gettypename(v_anydata));
end;
/
Running this code gives me the error "ORA-22370: incorrect usage of method ORA-22370 incorrect ussage of method ConvertCollection" (Yes, it actually repeats ORA-22370).
My question is: Is it possible to use ANYDATA on collections of rowtypes? I ask this because all examples I've seen of ANYDATA (so far) with collections use object types, none use rowtypes, but I haven't seen anything (yet) that explicitly says that rowtypes can't be used.
My goal was to clean up some very repetitive bulk-collect/insert code that does the same thing over and over, but with different cursors for different tables.
(Oracle 10g)
ANYDATA works with SQL data_types, i.e. anything you could use to define a table column.
%ROWTYPE is a PL/SQL construct, and so is not recognised by the SQL engine. If you think about the dynamic nature of %ROWTYPE you'll be able to figure out why.
Wanting to clean up repetitive code is a noble idea. I have previously implemented an ETL processor in SQL Types which used a supertype Object to own the generic processing, and subtypes to execute table specific code (such as inserts). These subtypes are completely generatable: not as slick as a dynamic %ROWTYPE implementation would have been, but still easy enough.
Platform: Oracle
Language: PL/SQL
Issue: Want to output a procedure OUT cursor into the SQLDeveloper SQLWosksheet.
Anyone know how to use the Oracle "Select * from Table( PipelinedFunction( Param ) ) " to check procedure code output cursors?
I am using Crsytal Reports off of an Oracle stored procedure. Crystal requires that a procedure return a cursor, which it fetchs and reads.
The procedure code I have is currently working, but I want to find the easiest way to view the effects of changes to the procedure code. I have SQLDeveloper available, and I'm doing my creation and sql testing in that. I would like to get a quick result visible in the SQL Developer Query Result window ("SQL Worksheet").
Is there a (simple) way to use a Function to read the cursor from the procedure? (and pipe that out to the Table function?)
Convoluted, I know, but I deal best when I can just see the results of code changes. If I can view the record results directly, it will speed up development of the report.
I know of the Table function and a little about pipelining in Oracle. I know a little about cursors in general and sys_refcursor. I know diddly about types and why I need them. (Isn't sys_regCursor supposed to get us away from that?)
The current procedure does an adequate but ungraceful series of queries, inserts to global temp tables (GTT), joins from GTT and original tables, more inserts, and more self-joins and then SELECTS the results into the OUT cursor. I might be able to do better relying on just cursors and such, but the current method is good enough to get results to the report.
I think I can handle SQL pretty well (for our purposes), but I am not an Oracle-specific developer... but I need help.
Anybody run across this? The whole idea was to speed my development for the procedure code, but I've spent a couple of days looking for a way to just get at the output... not what I had in mind.
Update:
I have tried some hare-brained schemes based on slivers that I've seen on the web... such as
Create or replace FUNCTION GET_BACKPLANE (
Node VARCHAR2 ) RETURN SYS_REFCURSOR
AS
RESULTS SYS_REFCURSOR;
BEGIN
Open Results for
Select Backplane(Results, Node) from Dual ;
... etc.
and
Create or replace Function GET_BACKPLANE (
NODE VARCHAR2 ) RETURN My_Table_Stru%ROWTYPE PIPELINED
AS
BEGIN ...
I don't think that Oracle is even considering letting me re-reference the output cursor from the procedure ("Results" is a sys_refcursor that holds the results of the last SELECT in the procedure). I don't know how to define it, open it, and reference it from the procedure.
I never got to the place where I could try
SELECT * FROM TABLE(GET_BACKPLANE( ... etc )
Sorry for any typos and bad Oracle Grammar... it's been a long several days.
SQL Developer allows us to use SQL*Plus commands in the Worksheet. So all you need to do is define a variable to hold the output of the ref cursor.
I may have misinterpreted the actual code you want to run but I'm assuming your actual program is a procedure Backplane(Results, Node) where results is an OUT parameter of datatype sys_refcursor and node is some input parameter.
var rc refcursor
exec Backplane(results=>:rc, Node=>42)
print rc
The output of the print statement is written to the Script Output pane.
Note that the use of SQL*Plus commands means we have to use the Run Script option F5 rather than execute statement.
Thanks for the help. In the end, I wound up brute-force-ing it...
Step by step:
Make a query, test a query,
create a global temp table from the structure,
add code to make another query off of that GTT, test the query,
create a global temp table from the structure,
etc.
In the end, I wound up running (anonymous block) scripts and checking the GTT contents at every stage.
The last part was to use the same last query from the original procedure, stuffing everything into the Cursor that crystal likes...
tomorrow, I test that.
But, I'll just force it through for the next procedure, and get it done in a day and a half instead of 2+ weeks (embarrassed).
Thanks,
Marc