I have a pretty generic/dynamic procedure where I pass in the table name as a parameter and execute queries dynamically using EXECUTE IMMEDIATE. I need to loop through a cursor and update each record. Is there a way to not have to hard code my table name??
I tried this but it doesn't work:
open cur for v_sql;
loop
fetch cur into v_recid;
EXIT WHEN cur%NOTFOUND;
EXECUTE IMMEDIATE 'update '||p_table||q'[ set status = 'I' where current of cur]';
end loop;
close cur;
SQL is a set oriented language. Your solution is row at a time or "slow at a time". I'd recommend spending your time to figure a way do not loop and do the update in a single statement.
Related
I have the following cursor in a procedure :
procedure Run is
Cur Cursor is select * from table where condition;
R Cur%rowtype;
Open Cur;
loop
fetch Cur into R;
exit when Cur%notfound;
-- Run some time consuming operations here
something...
end loop;
Close Cur;
end;
This cursor is run a scheduled job.
Assume when running this cursor there are 100 rows that satisfy the where condition.
If, while the procedure is running, I have a new rows inserted in the table that satisfies the same where condition, Is there any way that cursor picks also these new row please ?
Thanks.
Cheers,
No.
The set of rows the cursor will return is determined at the time the cursor is opened. At that point, Oracle knows the current SCN (system change number) and will return the data as it existed at that point in time.
Depending on the nature of the problem, you could write a loop that just keeps asking for a single row that meets the criteria (assuming your time-consuming operation updates some data so that you know what needs to be processed). Something like
loop
begin
select some_id
into l_some_id
from your_table
where needs_processing = 'Y'
order by some_id
fetch first row only;
exception
when no_data_found
then
l_some_id := null;
end;
exit when l_some_id is null;
some_slow_operation( l_some_id );
end loop;
assuming that some_slow_operation changes the needs_processing flag to N. And assuming that you are using the default read committed transaction isolation level.
You can have commit inside loop so that select query fetches latest records from table in every iteration.
No, a cursor can't do that. The transactions are consistent and your cursor is a snapshot of the data you've extracted.
If you want consistent results you could either:
Lock the table so that there will be no changes,
Use other mechanism e.g. move the logic to a trigger, which will execute on each new piece of data that satisfies your conditions (and bring overhead too so very situational)
So I have a block of PLSQL code that will drop all indexes as shown in the following block of code:
DECLARE
DRP_STMNT VARCHAR2(100) := '';
BEGIN
FOR I IN (SELECT INDEX_NAME FROM USER_INDEXES) LOOP
DRP_STMNT := 'DROP INDEX ' || I.INDEX_NAME;
EXECUTE IMMEDIATE DRP_STMNT;
END LOOP;
END;
/
That will do the job but should I use a cursor instead of embedding my SELECT statement within the FOR LOOP?
Does the FOR LOOP look at the entire table or does it process one row at a time?
What do you guys suggest using and why?
The result will be just the same.
Though, you'll consume some more energy as you'd have to type more characters as you have to declare a cursor and cursor variable, open a cursor, start the loop, fetch from it, take care about exiting the loop, close a cursor.
When you use a cursor FOR loop (as you did), there's much less typing as Oracle does lots of that for you. For free.
I have below query which I am trying to write in a procedure after begin clause. I dont want to use it as a cursor because of some dependency.
I want to make my db link dynamic instead of hardcoding it and for this reason i put my entire for loop in variable. If i take the variable out then my procedure is working fine. I dont want to change logic of my code while trying to make dblink dynamic.
But this part of loop is not working and throwing an error as
encounter the symbol end of the file when expecting one of the following:
PROCEDURE TMP_CHECK
IS
open CS for NESS_QUERY;
loop
fetch CS into REC;
exit when CS%notfound;
INSERT INTO TMP_Data(ID,NAME,ID_TST,CHK_DATE,VALUE,CHECK,SOURCE) VALUES
(IN_SEQ_NO,DB_NAME,DB_ID,REC.DAY_ID,REC.nb_ord,'ORDS','LEOSOFT');
COMMIT;
END LOOP;
CLOSE CS;
END LOOP;
END;
Dynamic SQL is hard because it turns compilation errors into runtime errors. It looks like your query has several compilation errors: duplicate table aliases, out-of-scope alias references, cross joins between the remote tables (unless that is deliberate, in which case yuck!). So the first thing to do is get the query running as straight SQL, only then make it dynamic.
Also don't include commented code in your template SQL. Things are already hard enough, why make them even harder by doing stuff like this?
ORDER BY
-- TE.market asc,
-- TE.entity asc,
TE.dayiid ASC)'
So, now we've got that out of the way let's look at the logic of what you're trying to do. We cannot drop dynamic segments of PL/SQL into a program. This just won't work ...
LQUERY='
FOR REC IN(
SELECT
... because you have not written a complete PL/SQL statement. But there is a way to do what you want: use a cursor variable. We can open a ref cursor for static and dynamic queries. Find out more.
The following is for illustrative purposes only: you haven't explained your business logic, so this is not necessarily the best way of doing things. But it should solve your immediate problem:
declare
....
l_order number;
l_dayiid number;
l_ety_id number;
rc sys_refcursor;
begin
...
FOR IIS_DB IN C_DB
LOOP
IN_DB_LINK:=LEO_DB.DATABASE_LINK;
IN_DAY:=LEO_DB.DAY_ID;
open rc for
'SELECT order,dayiid,ety_id
from ...
ORDER BY TE.dayiid ASC)';
loop
fetch rc into l_order, l_dayiid, l_ety_id;
exit when rc%notfound;
...
end loop;
close rc;
" PLS-00487: Invalid reference to variable 'REC'"
I think your problem is this:
fetch CS into REC;
You have defined REC as a string but clearly it should be a record type, which needs to match the projection of the query you're fetching. So you need to define something like this:
Type rec_t is record (
nb_ord number,
day_id number,
entity number
);
REC rec_t;
Now you can fetch a record into REC and reference its attributes.
Incidentally the nvl() you've written to supply NB_ORD is wrong. The first argument is the one you are testing for null: 500 will never be null so that's what you'll get for every row. You need to swap the parameters round.
Why Oracle made "where current of" syntax when you can use "rowid"? Example:
BEGIN
FOR rec IN (SELECT t.column1, t.rowid rid FROM test_table) LOOP
UPDATE test_table tb SET column1 = some_function(rec.column1) WHERE tb.rowid = rec.rid;
END LOOP;
COMMIT;
END;
DECLARE
CURSOR cur IS SELECT t.column1 FROM test_table;
param1 test_table.column1%TYPE;
BEGIN
LOOP
FETCH cur INTO param1;
UPDATE test_table tb SET tb.column1 = some_function(param1) WHERE CURRENT OF cur;
EXIT WHEN cur%NOTFOUND;
END LOOP;
COMMIT;
END;
Where Current Of is used to identify LAST FETCHED ROW in cursor. It's more safe, because You have 100% confidence, that f.e. You updating LAST FETCHED ROW from curosr. With Rowids there's danger, because it's really easy to mess up something.
Using WHERE CURRENT OF clause without having FOR UPDATE clause mentioned in your SELECT statement could be risky. Reason behind that is when you are not applying FOR UPDATE clause then you are not exclusively placing Row level lock to those rows which you are intending to update in the following UPDATE DML. And hence it opens an opportunity for outside world of violating data consistency i.e. some other user from different session may be looking to UPDATE same rows of your targeted table.
Also, in you learn more about WHERE CURRENT OF clause you will notice that during this clause Oracle internally makes use of ROWID's only to reach/identify the rows which needs to be updated.
Hope it helps !! Happy Programming
This question is similar to a couple others I have found on StackOverflow, but the differences are signficant enough to me to warrant a new question, so here it is:
I want to obtain a result set from dynamic SQL in Oracle and then display it as a result set in a SqlDeveloper-like tool, just as if I had executed the dynamic SQL statement directly. This is straightforward in SQL Server, so to be concrete, here is an example from SQL Server that returns a result set in SQL Server Management Studio or Query Explorer:
EXEC sp_executesql N'select * from countries'
Or more properly:
DECLARE #stmt nvarchar(100)
SET #stmt = N'select * from countries'
EXEC sp_executesql #stmt
The question "How to return a resultset / cursor from a Oracle PL/SQL anonymous block that executes Dynamic SQL?" addresses the first half of the problem--executing dynamic SQL into a cursor. The question "How to make Oracle procedure return result sets" provides a similar answer. Web search has revealed many variations of the same theme, all addressing just the first half of my question. I found this post explaining how to do it in SqlDeveloper, but that uses a bit of functionality of SqlDeveloper. I am actually using a custom query tool so I need the solution to be self-contained in the SQL code. This custom query tool similarly does not have the capability to show output of print (dbms_output.put_line) statements; it only displays result sets. Here is yet one more possible avenue using 'execute immediate...bulk collect', but this example again renders the results with a loop of dbms_output.put_line statements. This link attempts to address the topic but the question never quite got answered there either.
Assuming this is possible, I will add one more condition: I would like to do this without having to define a function or procedure (due to limited DB permissions). That is, I would like to execute a self-contained PL/SQL block containing dynamic SQL and return a result set in SqlDeveloper or a similar tool.
So to summarize:
I want to execute an arbitrary SQL statement (hence dynamic SQL).
The platform is Oracle.
The solution must be a PL/SQL block with no procedures or functions.
The output must be generated as a canonical result set; no print statements.
The output must render as a result set in SqlDeveloper without using any SqlDeveloper special functionality.
Any suggestions?
The closest thing I could think of is to create a dynamic view for which permission is required. This will certainly involve using a PL/SQL block and a SQL query and no procedure/function. But, any dynamic query can be converted and viewed from the Result Grid as it's going to be run as a select query.
DEFINE view_name = 'my_results_view';
SET FEEDBACK OFF
SET ECHO OFF
DECLARE
l_view_name VARCHAR2(40) := '&view_name';
l_query VARCHAR2(4000) := 'SELECT 1+level as id,
''TEXT''||level as text FROM DUAL ';
l_where_clause VARCHAR2(4000):=
' WHERE TRUNC(1.0) = 1 CONNECT BY LEVEL < 10';
BEGIN
EXECUTE IMMEDIATE 'CREATE OR REPLACE VIEW '
|| l_view_name
|| ' AS '
|| l_query
|| l_where_clause;
END;
/
select * from &view_name;
You seem to be asking for a chunk of PL/SQL code that will take an arbitrary query returning result set of undetermined structure and 'forward/restructure' that result set in some way such that is can easily be rendered by some "custom GUI tool".
If so, look into the DBMS_SQL for dynamic SQL. It has a DESCRIBE_COLUMNS procedure which returns the columns from a dynamic SELECT statement. The steps you would need are,
Parse the statement
Describe the result set (column names and data types)
Fetch each row, and for each column, call the datatype dependent function to return that value into a local variable
Place those local variables into a defined structure to return to the calling environment (eg consistent column names [such as col_1, col_2] probably all of VARCHAR2)
As an alternative, you could try building the query into an XMLFOREST statement, and parse the results out of the XML.
Added :
Unlike SQL Server, an Oracle PL/SQL call will not 'naturally' return a single result set. It can open up one or more ref cursors and pass them back to the client. It then becomes the client's responsibility to fetch records and columns from those ref cursors. If your client doesn't/can't deal with that, then you cannot use a PL/SQL call.
A stored function can return a pre-defined collection type, which can allow you to do something like "select * from table(func_name('select * from countries'))". However the function cannot do DML (update/delete/insert/merge) because it blows away any concept of consistency for that query. Plus the structure being returned is fixed so that
select * from table(func_name('select * from countries'))
must return the same set of columns (column names and data types) as
select * from table(func_name('select * from persons'))
It is possible, using DBMS_SQL or XMLFOREST, for such a function to take a dynamic query and restructure it into a pre-defined set of columns (col_1, col_2, etc) so that it can be returned in a consistent manner. But I can't see what the point of it would be.
Try try these.
DECLARE
TYPE EmpCurTyp IS REF CURSOR;
v_emp_cursor EmpCurTyp;
emp_record employees%ROWTYPE;
v_stmt_str VARCHAR2(200);
v_e_job employees.job%TYPE;
BEGIN
-- Dynamic SQL statement with placeholder:
v_stmt_str := 'SELECT * FROM employees WHERE job_id = :j';
-- Open cursor & specify bind argument in USING clause:
OPEN v_emp_cursor FOR v_stmt_str USING 'MANAGER';
-- Fetch rows from result set one at a time:
LOOP
FETCH v_emp_cursor INTO emp_record;
EXIT WHEN v_emp_cursor%NOTFOUND;
END LOOP;
-- Close cursor:
CLOSE v_emp_cursor;
END;
declare
v_rc sys_refcursor;
begin
v_rc := get_dept_emps(10); -- This returns an open cursor
dbms_output.put_line('Rows: '||v_rc%ROWCOUNT);
close v_rc;
end;
Find more examples here. http://forums.oracle.com/forums/thread.jspa?threadID=886365&tstart=0
In TOAD when executing the script below you will be prompted for the type of v_result. From the pick list of types select cursor, the results are then displayed in Toad's data grid (the excel spreadsheet like result). That said, when working with cursors as results you should always write two programs (the client and the server). In this case 'TOAD' will be the client.
DECLARE
v_result sys_refcursor;
v_dynamic_sql VARCHAR2 (4000);
BEGIN
v_dynamic_sql := 'SELECT * FROM user_objects where ' || ' 1 = 1';
OPEN :v_result FOR (v_dynamic_sql);
END;
There may be a similar mechanism in Oracle's SQL Developer to prompt for the binding as well.