Cursors How to step through the returned set of rows

Selected set When a Select statement is issued, the returned set is a set of rows. To step through, or process the rows in the set, it is necessary to be able to look at each one in turn. A CURSOR allows the user to iterate through the returned set.

Managing explicit cursors The cursor can be declared in any part of a PL/SQL block, subprogram or package. Within the program body, the cursor can be OPENed, FETCHed and CLOSEd. A cursor cannot be assigned a value or set of values – it must get its contents from a select statement.

Declaring a cursor CURSOR cursor_name [(parameter[, parameter]…)] [RETURN return_type] IS select_statement; Where –return_type is a record or row in a database table –Parameter is defined as: cursor_parameter)name [IN] datatype [{:= | DEFAULT} expression]

Example cursor declaration DECLARE CURSOR lateOrd IS SELECT supplierorderno, (delivereddate – supplierOrderDate) from sorder where (delivereddate – supplierOrderDate) > 5 or delivereddate is null; This cursor will contain a set of rows of supplier orders that either took more than 5 days to deliver, or have not been delivered. The scope of the cursor is the scope of the block in which it is declared.

Declaring the cursor with parameters DECLARE nodays integer; CURSOR lateOrd IS SELECT supplierorderno, (delivereddate – supplierOrderDate) from sorder where (delivereddate – supplierOrderDate) > nodays or delivereddate is null;

Opening and closing the cursor DECLARE CURSOR lateOrd IS SELECT … … BEGIN OPEN lateOrd; … CLOSE lateOrd; END; This opens the cursor, but doesn’t fill it. If it is a parameterised cursor, it could be: OPEN lateOrd(3);

Fetching the cursor DECLARE CURSOR lateOrd IS SELECT supplierorderno, (delivereddate - supplierOrderDate) from sorder where (delivereddate - supplierOrderDate) > 5 or delivereddate is null; LocOrdNo sOrder.SupplierORDERNO%Type; DaysLate Integer; BEGIN OPEN lateOrd; LOOP FETCH lateOrd into LocOrdNo, DaysLate; EXIT WHEN lateOrd%NOTFOUND; dbms_output.put_line ('Order number '||LocOrdNo||' was delivered '||DaysLate||' days late.'); End Loop; Close LateOrd; END;

Fetching Fetch retrieves the rows one at a time from the result set. The named exceptions relating to cursors are: –%found, %notfound, %rowcount and %isopen. –These do not automatically raise an exception, so you must test for them.

Cursor loop Open LateOrd; LOOP FETCH lateOrd INTO LocOrdNo, DaysLate; dbms_output.put_line (lateOrd%rowcount||’. Order number ’||LocOrdNo||’ was ‘||DaysLate||’ days late.’); END LOOP; Dbms_output.put_line (‘Altogether, there were || LateOrd%rowcount||’ late orders’); Close LateOrd; This numbers the late orders.

Other Cursor qualities The implicit For loop can open the cursor, fetch each item individually and then close it (see next slide). Instead of having to itemise the columns in the table, we can declare a cursor row type: Declare cursor s1 is … s1_rec s1%rowtype;

Cursors for update I want to up the cost price of all stock items that are supplied by supplier number 101 by 10%. Declare cursor s1 is select * from stock where supplier_Id = 501 for update; s1_rec s1%rowtype; Begin for s1_rec in s1 loop update stock set unitcostprice = unitcostprice * 1.1 where current of s1; end loop; commit; End;