I have a procedure which returns ref cursor as output parameter. I need to find a way to get the count of no.of records in the cursor. Currently I have count fetched by repeating the same select query which is hindering the performance.
ex:
create or replace package temp
TYPE metacur IS REF CURSOR;
PROCEDURE prcSumm (
pStartDate IN DATE,
pEndDate IN DATE,
pKey IN NUMBER,
pCursor OUT metacur
) ;
package body temp is
procedure prcSumm(
pStartDate IN DATE,
pEndDate IN DATE,
pKey IN NUMBER,
pCursor OUT metacur
)
IS
vCount NUMBER;
BEGIN
vCount := 0;
select count(*) into vCount
from customer c, program p, custprog cp
where c.custno = cp.custno
and cp.programid = p.programid
and p.programid = pKey
and c.lastupdate >= pStartDate
and c.lastupdate < pEndDate;
OPEN pCursor for SELECT
c.custno, p.programid, c.fname, c.lname, c.address1, c.address2, cp.plan
from customer c, program p, custprog cp
where c.custno = cp.custno
and cp.programid = p.programid
and p.programid = pKey
and c.lastupdate >= pStartDate
and c.lastupdate < pEndDate;
end prcSumm;
Is there a way to get the no.of rows in the out cursor into vCount.
Thanks!
Oracle does not, in general, know how many rows will be fetched from a cursor until the last fetch finds no more rows to return. Since Oracle doesn't know how many rows will be returned, you can't either without fetching all the rows (as you're doing here when you re-run the query).
Unless you are using a single-user system or you are using a non-default transaction isolation level (which would introduce additional complications), there is no guarantee that the number of rows that your cursor will return and the count(*) the second query returns would match. It is entirely possible that another session committed a change between the time that you opened the cursor and the time that you ran the count(*).
If you are really determined to produce an accurate count, you could add a cnt column defined as count(*) over () to the query you're using to open the cursor. Every row in the cursor would then have a column cnt which would tell you the total number of rows that will be returned. Oracle has to do more work to generate the cnt but it's less work than running the same query twice.
Architecturally, though, it doesn't make sense to return a result and a count from the same piece of code. Determining the count is something that the caller should be responsible for since the caller has to be able to iterate through the results. Every caller should be able to handle the obvious boundary cases (i.e. the query returns 0 rows) without needing a separate count. And every caller should be able to iterate through the results without needing to know how many results there will be. Every single time I've seen someone try to follow the pattern of returning a cursor and a count, the correct answer has been to redesign the procedure and fix whatever error on the caller prompted the design.
Related
I have the following function, which returns the next available client ID from the Client table:
CREATE OR REPLACE FUNCTION getNextClientID RETURN INT AS
ctr INT;
BEGIN
SELECT MAX(NUM) INTO ctr FROM Client;
IF SQL%NOTFOUND THEN
RETURN 1;
ELSIF SQL%FOUND THEN
-- RETURN SQL%ROWCOUNT;
RAISE_APPLICATION_ERROR(-20010, 'ROWS FOUND!');
-- RETURN ctr + 1;
END IF;
END;
But when calling this function,
BEGIN
DBMS_OUTPUT.PUT_LINE(getNextClientID());
END;
I get the following result:
which I found a bit odd, since the Client table contains no data:
Also, if I comment out RAISE_APPLICATION_ERROR(-20010, 'ROWS FOUND!'); & log the value of SQL%ROWCOUNT to the console, I get 1 as a result.
On the other hand, when changing
SELECT MAX(NUM) INTO ctr FROM Client;
to
SELECT NUM INTO ctr FROM Client;
The execution went as expected. What is the reason behind this behavior ?
Aggregate functions will always return a result:
All aggregate functions except COUNT(*), GROUPING, and GROUPING_ID
ignore nulls. You can use the NVL function in the argument to an
aggregate function to substitute a value for a null. COUNT and
REGR_COUNT never return null, but return either a number or zero. For
all the remaining aggregate functions, if the data set contains no
rows, or contains only rows with nulls as arguments to the aggregate
function, then the function returns null.
You can change your query to:
SELECT COALESCE(MAX(num), 1) INTO ctr FROM Client;
and remove the conditionals altogether. Be careful about concurrency issues though if you do not use SELECT FOR UPDATE.
Query with any aggregate function and without GROUP BY clause always returns 1 row. If you want no_data_found exception on empty table, add GROUP BY clause or remove max:
SQL> create table t (id number, client_id number);
Table created.
SQL> select nvl(max(id), 0) from t;
NVL(MAX(ID),0)
--------------
0
SQL> select nvl(max(id), 0) from t group by client_id;
no rows selected
Usually queries like yours (with max and without group by) are used to avoid no_data_found.
Agregate functions like MAX will always return a row. It will return one row with a null value if no row is found.
By the way SELECT NUM INTO ctr FROM Client; will raise an exception where there's more than one row in the table.
You should instead check whether or not ctr is null.
Others have already explained the reason why your code isn't "working", so I'm not going to be doing that.
You seem to be instituting an identity column of some description yourself, probably in order to support a surrogate key. Doing this yourself is dangerous and could cause large issues in your application.
You don't need to implement identity columns yourself. From Oracle 12c onwards Oracle has native support for identity columns, these are implemented using sequences, which are available in 12c and previous versions.
A sequence is a database object that is guaranteed to provide a new, unique, number when called, no matter the number of concurrent sessions requesting values. Your current approach is extremely vulnerable to collision when used by multiple sessions. Imagine 2 sessions simultaneously finding the largest value in the table; they then both add one to this value and try to write this new value back. Only one can be correct.
See How to create id with AUTO_INCREMENT on Oracle?
Basically, if you use a sequence then you don't need any of this code.
As a secondary note your statement at the top is incorrect:
I have the following function, which returns the next available client ID from the Client table
Your function returns the maximum ID + 1. If there's a gap in the IDs, i.e. 1, 2, 3, 5 then the "missing" number (4 in this case) will not be returned. A gap can occur for any number of reasons (deletion of a row for example) and does not have a negative impact on your database in any way at all - don't worry about them.
I recently started studying PL/SQL and I found myself with this problem. I have a cursor that has the data for a specific person selected via code from another table. I'm fetching all the months with the salary of that person and outputting them. Now I need to make an avg() of all of the salaries. How do I do that ? Can I get only that column from the cursor. I could have counted the rows and divided the total sum of the salaries on that count and I can make another select but is there any faster way ?
You don't need cursor to get average salary as single value. You need to use aggregate functions. And even if you needed a cursor to, lets say, return data to calling code, you still use aggregate function to calculate averages and return cursor of that.
This is just an example
Declare
v_avgSal employees.salary%TYPE;
Begin
SELECT AVG(salary) into v_avgSal
FROM employees
WHERE employee_id = 10 And
(payDate >= To_Date('01012015', 'MMDDYYYY') AND payDate < To_Date('01012016', 'MMDDYYYY'));
Dbms_Output.Put_Line(v_avgSal);
End;
I'm here because i could not finde anywhere else if there is a way to return the previous value in a loop (Cursor) to compare with the current value, for instance..
Cursor.Value = Cursor-1.Value;
It's bacause i have several contract numbers that i need to send by mail to the Business sector, but, in order to resume all the rows i want to compare if the current contract number are the same as the last contract number and validate it to dont send duplicated contract numbers.
Exemple of Record that i to skip in order to send no duplicate "Order Numbers": (Order_Number is my Key, not a sequencial numeric id):
cCursor.Value = cCursor-1.Value
cCursor.(111) = cCursor-1.(111)
Exemple of Record that i want to save in order to send as a processed "Order Number": (Order_Number is my Key, not a sequencial numeric id):
cCursor.Value = cCursor-1.Value
cCursor.(132) = cCursor-1.(111)
My Regards.
You cant reference backwards. Th easiest alternative is to store the key value (contract_id) in a variable and have logic like:
DECLARE
CURSOR c1 IS .....;
vLastContractID NUMBER := 0;
BEGIN
FOR r1 IN c1 LOOP
IF vLastContractID != r1.CONTRACT_ID THEN
-- do something
vLastContractID := r1.CONTRACT_ID;
END IF;
END LOOP;
END;
It's not entirely clear what you are asking.
A cursor is a forward-only structure. You cannot fetch a prior row, just the next row (or set of rows). Your query, however, can certainly include data from prior rows using the lag function. For example, this will show you the ename for the prior row in your result
SELECT empno, ename, lag(ename) over (order by empno) prior_ename
FROM emp
ORDER BY empno
In a PL/SQL loop, you can also obviously have a local variable that has the data from the previous row that was fetched and use that to compare against the data from the most current row.
Please use ANALYTICAL function to check for prior or post rows. LEAD,LAG functions are best way to do this.
I'm trying to build a PL/SQL application to mine frequent item sets out of a set of given data and I've run into a bit of a snag. My PL/SQL skills aren't as good as I'd like them to be, so perhaps one of you can help me understand this a bit better.
So to begin, I'm using the Oracle data mining procedure: *DBMS_FREQUENT_ITEMSET.FI_TRANSACTIONAL*
While reading the documentation, I came across the following example which I have manipulated to query over my data set:
CREATE OR REPLACE TYPE FI_VARCHAR_NT AS TABLE OF NUMBER;
/
CREATE TYPE fi_res AS OBJECT (
itemset FI_VARCHAR_NT,
support NUMBER,
length NUMBER,
total_tranx NUMBER
);
/
CREATE TYPE fi_coll AS TABLE OF fi_res;
/
create or replace
PROCEDURE freq_itemset_test is
cursor freqC is
SELECT itemset
FROM table(
CAST(DBMS_FREQUENT_ITEMSET.FI_TRANSACTIONAL(CURSOR(SELECT sale.customerid, sale.productid FROM Sale INNER JOIN Customer ON customer.customerid = sale.customerid WHERE customer.region = 'Canada' )
,0,2, 2, NULL, NULL) AS fi_coll));
coll_nt FI_VARCHAR_NT;
num_rows int;
num_itms int;
BEGIN
num_rows := 0;
num_itms := 0;
OPEN freqC;
LOOP
FETCH freqC INTO coll_nt;
EXIT WHEN freqC%NOTFOUND;
num_rows := num_rows + 1;
num_itms := num_itms + coll_nt.count;
END LOOP;
DBMS_OUTPUT.PUT_LINE('Rows: ' || num_rows || ' Columns: ' || num_itms);
CLOSE freqC;
END;
My reasoning for using the Oracle FI_TRANSACTIONAL over straight SQL is that I will need to repeat this analysis for multiple dynamic values of K, so why reinvent the wheel? Ultimately, my goal is to reference each individual item sets returned by the procedure and return the set with the highest support based on some query logic. I will be incorporating this block of PL/SQL into another that basically changes the literal in the query from 'Canada' to multiple other regions based on the content of the data.
My question is: How can I actually get a programmatic reference on the data returned by the cursor (freqC)? Obviously I do not need to count the rows and columns, but that was part of the example. I'd like to print out the item sets with DBMS print line after I've found the most occurring item set. When I view this in a debugger, I see that each fetch of the cursor actually returns an item set (in this case, k=2, so two items). But how do I actually touch them programmatically? I'd like to grab the sets themselves as well as fi_res.support.
As always, thanks to everyone for sharing their brilliance!
You are fetching your data into a nested table. So to see the data in there, you would need to loop over the nested table:
FOR i IN coll_nt.FIRST .. coll_nt.LAST
LOOP
dbms_output.put_line(i||': '||coll_nt(i));
END LOOP;
For much more information on nested tables and other types of collections, see the presentation at:
http://www.toadworld.com/platforms/oracle/w/wiki/8253.everything-you-need-to-know-about-collections-but-were-afraid-to-ask.aspx
I have a query that in the select statement uses a custom built function to return one of the values.
The problem I have is every now and then this function will error out because it returns more than one row of information. SQL Error: ORA-01422: exact fetch returns more than requested number of rows
To further compound the issue I have checked the table data within the range that this query should be running and can't find any rows that would duplicate based on the where clause of this Function.
So I would like a quick way to identify on which Row of the original query this crashes so that I can take the values from that query that would be passed into the function and rebuild the Functions query with these values to get it's result and see which two or more rows are returned.
Any ideas? I was hoping there could be a way to force Oracle to process one row at a time until it errors so you can see the results UP to the first error.
Added the code:
FUNCTION EFFPEG
--Returns Effective Pegged Freight given a Effdate, ShipTo, Item
DATE1 IN NUMBER -- Effective Date (JULIANDATE)
, SHAN IN NUMBER -- ShipTo Number (Numeric)
, ITM IN NUMBER -- Short Item Number (Numeric)
, AST IN VARCHAR -- Advance Pricing type (varchar)
, MCU IN VARCHAR Default Null --ShipFrom Plant (varchar)
) RETURN Number
IS
vReturn Number;
BEGIN
Select ADFVTR/10000
into vReturn
from PRODDTA.F4072
where ADEFTJ <= DATE1
and ADEXDJ >= DATE1
and ADAN8 = SHAN and ADITM = ITM
and TRIM(ADAST) = TRIM(AST)
and ADEXDJ = (
Select min(ADEXDJ) ADEXDJ
from PRODDTA.F4072
where ADEFTJ <= DATE1
and ADEXDJ >= DATE1
and ADAN8 = SHAN
and ADITM = ITM
and TRIM(ADAST) = TRIM(AST));
Query that calls this code and passes in the values is:
select GLEXR, ORDTYPE,
EFFPEG(SDADDJ, SDSHAN, SDITM, 'PEGFRTT', SDMCU),
from proddta.F42119
I think the best way to do it is trough Exceptions.
What you need to do is to add the code to handle many rows exception in your function:
EXCEPTION
WHEN TOO_MANY_ROWS THEN
INSERT INTO ERR_TABLE
SELECT your_columns
FROM query_that_sometimes_returns_multiple_rows
In this example the doubled result will go to separated table or you can decide to simply print out with dbms_output.
An easy page to start can be this, then just google exception and you should be able to find all you need.
Hope this can help.