Automatically inserting data into a table using a procedure - oracle

Question

I would like to ask you a rather easy question but I cannot get my head around it as I am a beginner in SQL.
My task is: Enter initial data into BankStats2 by inserting rows into BankStats2 that
contain the branch names together with how many loans are in the Loan
table for that branch name.
desc BankStats2
Name Null? Type
----------------------------------------- -------- ----------------------------
BRANCHNAME NOT NULL VARCHAR2(20)
NUMBEROFLOANS NUMBER(38)
desc Loan
Name Null? Type
----------------------------------------- -------- ----------------------------
CUSTOMERNAME CHAR(20)
BRANCHNAME CHAR(20)
AMOUNT NUMBER(38)
LOANNUMBER NOT NULL NUMBER(38)
select branchName,count(customerName) from Loan group by branchName;
BRANCHNAME COUNT(CUSTOMERNAME)
-------------------- -------------------
Yorkshire 3
RoyalBank 1
Midlands 3
Basically, I would like to insert this information in the BankStats2 table and the way I thought of doing it is by creating a procedure which I will show below.
CREATE OR REPLACE PROCEDURE PopulateBankStats AS
CURSOR someLoanRows IS
SELECT branchName,COUNT(customerName) FROM loan GROUP BY branchName;
aBranchNameRow loan.branchName%TYPE;
numberOfLoans INT;
BEGIN
OPEN someLoanRows;
LOOP
FETCH someLoanRows INTO aBranchNameRow, numberOfLoans;
INSERT INTO BankStats2 VALUES (aBranchNameRow,numberOfLoans);
EXIT WHEN someLoanRows%NOTFOUND;
END LOOP;
CLOSE someLoanRows;
END;
/
But executing it give me the following error:
ERROR at line 1:
ORA-00001: unique constraint (N0757934.SYS_C0034405) violated
ORA-06512: at "N0757934.POPULATEBANKSTATS", line 10
ORA-06512: at line 1
Any help would be greatly appreciated. Thank you for your time!

Answer 1

This insert fails: INSERT INTO BankStats2 VALUES (aBranchNameRow,numberOfLoans); due to the error: ORA-00001: unique constraint (N0757934.SYS_C0034405) violated
This means that there is an unique constraint created on some of the columns of the table BankStats2.
In order to find which column has unique constraint, run this query:
select * from USER_IND_COLUMNS where index_name = 'SYS_C0034405';
Your procedure is trying to insert a record with a value of this column which already is existing in the table.

Answer 2

Have a look on the INSERT statement.
What your procedure is doing is exactly this insert statement:
INSERT INTO BankStats2 (BRANCHNAME,NUMBEROFLOANS)
SELECT branchName,COUNT(customerName) FROM loan GROUP BY branchName;
It is always preferable to use SQL statement (if possible) instead of the PL/SQL cursor loop logik - search Tom Kyte's "row by row - slow by slow" for an explantion.
Even if you want to use a procedure at all cost - use this INSERT in the preocedure.
Your exception means that you try to insert a value of the column BRANCHNAME that already exists in the table BankStats2.
This could be by an accident or a systematic problem.
If it is an accident, simple clean the data, i.e. DELETE the row(s) with the corresponding keys from the BankStats2 table.
This query returns the values existing in both tables
select BRANCHNAME from BankStats2
intersect
select branchName FROM loan;
If you want to systematically avoid inserting the duplicated row, add this logik in your INSERT statement:
INSERT INTO BankStats2 (BRANCHNAME,NUMBEROFLOANS)
SELECT branchName,COUNT(customerName)
FROM loan
WHERE branchName IS NOT NULL
and branchName NOT IN (select BRANCHNAME from BankStats2)
GROUP BY branchName;
Note that the SELECT excludes the row with the value that already exists in the target table - using NOT IN (subquery).
Note also that I'm approaching your next possible problem. The column BRANCHNAME is non nullable in BankStats2, but is nullable (i.e. may contain NULL) in loan, so you would fail to insert the row with NULL to the table BankStats2. Therefore I exclude those rows with the branchName IS NOT NULL predicate.
If you want to process the existing keys with an UPDATE logik, check the MERGE statement.