PL_SQL Explanation of DISPCUST.SQL

1 of 3 DECLARE cnum builder.customer.customer_id%type; cname builder.customer.customer_name%type; caddr builder.customer.customer_address%type; status boolean; procedure get_cust_details ( cust_noin builder.customer.customer_id%type, cust_name out builder.customer.customer_name%type, cust_addrout builder.customer.customer_address%type, status outboolean) is

Part 1 – declarations Formal parameters: The first three parameters take their type from the data definitions in the builder.customer table (i.e. the customer table in the builder schema). Cust_no –This allocates a slot for the customer id to be passed into the procedure. Cust_name –This allocates a slot for the customer name to be returned from the procedure, having been read from the customer table. Cust_addr –This allocates a slot for the customer address to be returned from the procedure, having been read from the customer table. Status –This returns a value to show how the procedure finished.

part 2 of 3 begin status := true; select builder.customer.customer_name, builder.customer.customer_address into cust_name, cust_addr from builder.customer where builder.customer.customer_id = cust_no Exception when no_data_found then dbms_output.put_line('ERROR'); status := false; end;

Part 2 – procedure content. Initially, we assume the procedure will work. Using the cust_no passed across, we select the customer’s name and address from the customer table. If this works, the status is left as at ‘true’. If it fails, it triggers an exception. The exception ‘ no_data_found’ then sets the status to ‘false’.

Part 3 of 3 begin cnum:=1; get_cust_details(cnum,cname, caddr, status); dbms_output.enable; if (status) then dbms_output.put_line('status = true'); dbms_output.put('customer number ='); dbms_output.put_line (cnum || ' ' || cname || ' ' || caddr); else dbms_output.put_line('status = false'); dbms_output.put_line ('Customer ' || cnum || ' not found'); end if; end;

Part 3 – main program We initialise the value of CNUM to 1 We call cust_details, replacing the formal parameters as follows: –Cnum fills the slot cust_no –Cname takes its value from cust_name –Caddr takes its value from cust_addr –Status takes its value from status. The procedure outputs the customer details in a concatenated string.

Exceptions There can be several different types of exceptions. The ‘catch-all’ exception handler is –When others then… –This neatly exits from any error condition.

Commit and Rollback When updating, inserting or deleting, the user has the chance to commit data at certain checkpoints. This allows the user to conduct quite a complex transaction, without fully saving data to the database. –If the transaction completes successfully, then the data can be COMMITted. –If the transaction fails, the user can initiate a ROLLBACK, which cancels everything since the last commit.

Builder schema tables

Update procedures Write a procedure to increase the cost and retail price of all stock from a given supplier by x%. Specification: –We need to know: Who the supplier is What the percentage is. –We need to change: The unitprice and the unitcostprice for all stock supplied by that supplier. –We need to confirm: That the procedure has completed successfully and COMMITed the data.