The flow chart in Figure 6-5 summarizes the functionality
of program cex8. This program uses a cursor and the UPDATE WHERE
CURRENT command to update column ReceivedQty in table
PurchDB.OrderItems. The runtime dialog for cex8
appears in Figure 6-6, and the source code in Figure 6-7.
The program first executes function
DeclareCursor 26 , which
contains the DECLARE CURSOR command 7 . This
command is a preprocessor directive and is not executed at run time.
At run time, function DeclareCursor only displays the message
Declare the Cursor. The DECLARE CURSOR command defines a cursor
named OrderReview. The cursor is associated with a SELECT
command that retrieves the following columns for all rows in
table PurchDB.OrderItems having a specific order number but
no null values in column VendPartNumber:
OrderNumber (defined NOT NULL)
ItemNumber (defined NOT NULL)
VendPartNumber
ReceivedQty
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Cursor OrderReview has a FOR UPDATE clause naming column
ReceivedQty to allow the user to change the value in this
column.
To establish a DBE session, program cex8 executes function
ConnectDBE 27 . This function evaluates to TRUE when
the
CONNECT command 1 for the
sample DBEnvironment, PartsDBE, is
successfully executed.
The program then executes function FetchUpdate
until the Done flag
is set to TRUE 28 .
Function FetchUpdate prompts for an order number or a
zero 17 . When the user enters a zero,
function FetchUpdate ends and the main program prompts the
user to indicate whether another OrderNumber should be FETCHed.
When the user enters
an order number, the program begins a transaction by executing
function BeginTransaction 18 , which executes the
BEGIN WORK command 3 .
Cursor OrderReview is then opened by invoking function
OpenCursor 19 . This function, which executes the OPEN
command 8 , evaluates to TRUE when the command is successful.
A row at a time is retrieved and optionally updated until
the DoFetch flag
is set to FALSE 20 . This flag becomes false when:
The FETCH command fails. This command fails when no rows
qualify for the active set, when the last row has already been
fetched, or when ALLBASE/SQL cannot execute this command for some
other reason.
The program user wants to stop reviewing rows from the active set.
The FETCH command 21 names an indicator variable for
ReceivedQty, the only column
in the query result that may contain
a null value. If the FETCH command is successful, the program
executes function DisplayUpdate
22 to display the current
row and optionally update it.
Function DisplayUpdate executes function
DisplayRow 10 to display
the current row 6 . If column
ReceivedQty in the current row contains a null value, the
message, ReceivedQty is NULL, is displayed.
Function DisplayUpdate then prompts whether the user
wants to update the current ReceivedQty value 11 . If so,
the user is prompted for a new value. The value accepted is used
in an UPDATE WHERE CURRENT command 12 .
If the user entered a zero, a null value is assigned to this
column.
The program then prompts whether to FETCH another row 13 . If
so, the FETCH command is re-executed. If not, the program
prompts the user whether to make permanent any updates that
may have made made to the active set 14 . To keep any row
changes, the program executes function EndTransaction 16
which executes the COMMIT WORK command 4 . To undo any row
changes, the program executes function RollBack 15 ,
which executes the ROLLBACK WORK command 5 .
The COMMIT WORK command is also executed
when ALLBASE/SQL sets sqlca.sqlcode to
100 following execution of the FETCH command 23 .
Sqlca.sqlcode is set to 100 when
no rows qualify for the active set or when the last row has
already been fetched. If the FETCH command fails for some other
reason, the ROLLBACK WORK command is executed instead 24 .
Before any COMMIT WORK or ROLLBACK WORK command is executed,
cursor OrderReview is closed 9 .
Although the cursor is automatically closed whenever a
transaction is terminated, it is good programming practice to
use the CLOSE command to close open cursors prior to terminating
transactions.
When the program user enters an N in response to the main program's
prompt to FETCH another order number, the program
terminates by executing function ReleaseDBE 29 ,
which executes the RELEASE command 2 .
Figure 6-5 Flow Chart of Program cex8
![[Flow Chart of Program cex8]](img/124_009.gif)
Figure 6-6 Runtime Dialog of Program cex8
Program to UPDATE OrderItems Table via a CURSOR - cex8
Event List:
CONNECT TO PartsDBE
Prompt for Order Number
BEGIN WORK
OPEN CURSOR
FETCH a row
Display the retrieved row
Prompt for new Received Quantity
UPDATE row within OrderItems table
FETCH the next row, if any, with the same Order Number
Repeat the above five steps until there are no more rows
CLOSE CURSOR
End Transaction
Repeat the above eleven steps until user enters 0
RELEASE the DBEnvironment
Connect to PartsDBE
Declare Cursor
Enter OrderNumber or 0 to STOP > 30520
Begin Work
Open the Cursor
Fetch the next row.
Order Number: 30520
Item Number: 1
Vendor Part Number: 9375
Received Quantity: 9
Do you want to change ReceivedQty (Y/N)? > n
Do you want to see another row (Y/N)? > y
Fetch the next row.
Order Number: 30520
Item Number: 2
Vendor Part Number: 9105
Received Quantity: 3
Do you want to change ReceivedQty (Y/N)? > y
Enter New ReceivedQty or 0 for NULL > 15
Update the PurchDB.OrderItems table
Do you want to see another row (Y/N)? > y
Fetch the next row.
Order Number: 30520
Item Number: 3
Vendor Part Number: 9135
Received Quantity: 3
Do you want to change ReceivedQty (Y/N)? > n
Do you want to see another row (Y/N)? > y
Fetch the next row.
Row not found or no more rows!
Do you want to save your changes (Y/N)? > y
Close the Cursor
Commit Work
1 rows changed!
Do you want to FETCH another OrderNumber (Y/N)? > y
Enter an OrderNumber or a 0 to STOP > 30510
Begin Work
Open the Cursor
Fetch the next row.
Order Number: 30510
Item Number: 1
Vendor Part Number: 1001
Received Quantity: 3
Do you want to change ReceivedQty (Y/N)? > n
Do you want to see another row (Y/N)? > n
Close Cursor
Commit Work
Do you want to FETCH another OrderNumber (Y/N)? > n
Release PartsDBE
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Figure 6-7 Program cex8: Using UPDATE WHERE CURRENT
/* Program cex8 */
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/* This program illustrates the use of SQL's UPDATE WHERE */
/* CURRENT command using a cursor to update a single row */
/* at a time. */
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
typedef int boolean;
boolean Abort;
boolean Done;
boolean DoFetch;
char response[2];
int RowCounter;
#include <stdio.h>
#define OK 0
#define NotFound 100
#define MultipleRows -10002
#define DeadLock -14024
#define FALSE 0
#define TRUE 1
sqlca_type sqlca; /* SQL Communication Area */
/* Begin Host Variable Declarations */
EXEC SQL BEGIN DECLARE SECTION;
int OrderNumber;
int ItemNumber;
char VendPartNumber[17];
int ReceivedQty;
sqlind ReceivedQtyInd;
char SQLMessage[133];
EXEC SQL END DECLARE SECTION;
/* End Host Variable Declarations */
int SQLStatusCheck() /* Function to Display Error Messages */
{
Abort = FALSE;
if (sqlca.sqlcode < DeadLock) Abort = TRUE;|
do {
EXEC SQL SQLEXPLAIN :SQLMessage;
printf("\n");
printf("%s\n",SQLMessage);
} while (sqlca.sqlcode != 0);
if (Abort) {
ReleaseDBE();
}
} /* End SQLStatusCheck Function */
boolean ConnectDBE() /* Function to Connect to PartsDBE */
27
{
boolean ConnectDBE;
printf("\n Connect to PartsDBE");
EXEC SQL CONNECT TO 'PartsDBE'; 1
ConnectDBE = TRUE;
if (sqlca.sqlcode != OK) {
ConnectDBE = FALSE;
SQLStatusCheck();
} /* End if */
return (ConnectDBE);
} /* End of ConnectDBE Function */
int ReleaseDBE() /* Function to Release PartsDBE */
29
{
printf("\n Release PartsDBE");
printf("\n");
EXEC SQL RELEASE; 2
Done = TRUE;
if (sqlca.sqlcode != OK) SQLStatusCheck();
} /* End ReleaseDBE Function */
boolean BeginTransaction() /* Function to Begin Work */ 18
{
boolean BeginTransaction;
printf("\n");
printf("\n Begin Work");
EXEC SQL BEGIN WORK; 3
if (sqlca.sqlcode != OK) {
SQLStatusCheck();
ReleaseDBE();
}
} /* End BeginTransaction Function */
int EndTransaction() /* Function to Commit Work */ 16
{
printf("\n");
printf("\n Commit Work");
EXEC SQL COMMIT WORK; 4
if (sqlca.sqlcode != OK) {
SQLStatusCheck();
ReleaseDBE();
}
} /* End EndTransaction Function */
int RollBack() /* Function to RollBack work */ 15
{
printf("\n");
printf("\n RollBack Work");
EXEC SQL ROLLBACK WORK; 5
if (sqlca.sqlcode != OK) {
SQLStatusCheck();
ReleaseDBE();
}
} /* End of RollBack Function */
int DisplayRow() /* Function to Display Parts Table Rows */ 10
{
printf("\n");
printf("Order Number: %10d\n", OrderNumber); 6
printf("Item Number: %10d\n", ItemNumber);
printf("Vendor Part Number: %s\n", VendPartNumber);
if (ReceivedQtyInd != 0)
printf("Received Quantity: is NULL \n");
else
printf("Received Quantity: %5d\n", ReceivedQty);
} /* End of DisplayRow */
int DeclareCursor() /* Function to Declare the Cursor */ 26
{
printf("\n");
printf("\n Declare the Cursor");
EXEC SQL DECLARE OrderReview 7
CURSOR FOR
SELECT OrderNumber,
ItemNumber,
VendPartNumber,
ReceivedQty
FROM PurchDB.OrderItems
WHERE OrderNumber = :OrderNumber
AND VendPartNumber IS NOT NULL
FOR UPDATE OF ReceivedQty;
} /* End DeclareCursor Function */
boolean OpenCursor() /* Function to Open the Declared Cursor */
19
{
boolean OpenCursor;
OpenCursor = TRUE;
printf("\n");
printf("\n Open the Cursor");
EXEC SQL OPEN OrderReview; 8
if (sqlca.sqlcode != OK) {
OpenCursor = FALSE;
SQLStatusCheck();
RollBack();
}
return(OpenCursor);
} /* End of OpenCursor Function */
int CloseCursor() /* Function to Close the Declared Cursor */
{
printf("\n");
printf("\n Close the Cursor");
EXEC SQL CLOSE OrderReview;
if (sqlca.sqlcode != OK) {
SQLStatusCheck();
EndTransaction();
}
} /* End of CloseCursor Function */
int DisplayUpdate() /* Display & Update row in OrderItems Table*/
{ 22
DisplayRow(); 10
printf("\n");
printf("\n Do you want to change ReceivedQty (Y/N)? > "); 11
scanf("%s",response);
if ((response[0] == 'Y') || (response[0] == 'y')) {
printf("\n");
printf("\n Enter new ReceivedQty or a 0 for NULL > ");
scanf("%d5",&ReceivedQty);
if (ReceivedQty == 0)
ReceivedQtyInd = -1;
else
ReceivedQtyInd = 0;
printf("\n UPDATE the PurchDB.OrderItems table");
EXEC SQL UPDATE PurchDB.OrderItems 12
SET ReceivedQty = :ReceivedQty :ReceivedQtyInd
WHERE CURRENT OF OrderReview;
if (sqlca.sqlcode != OK)
SQLStatusCheck();
else
RowCounter = RowCounter + 1;
}
printf("\n");
printf("\n Do you want to see another row (Y/N)? > "); 13
scanf("%s",response);
if ((response[0] == 'N') || (response[0] == 'n')) {
if (RowCounter > 0) {
printf("\n");
printf("\n Do you want to save the changes you made (Y/N)?>");
scanf("%s",response); 14
if ((response[0] == 'N') || (response[0] == 'n')) {
CloseCursor();
RollBack(); 15
DoFetch = FALSE;
}
else {
CloseCursor();
EndTransaction(); 16
printf(RowCounter," %d\n rows were changed!");
DoFetch = FALSE;
}
}
if (RowCounter == 0) {
CloseCursor();
EndTransaction();
DoFetch = FALSE;
}
}
} /* End DisplayUpdate Function */
int FetchUpdate() /* Fetch a row to Update within OrderItems */
{ 28
printf("\n");
printf("\n Enter an OrderNumber or a 0 to STOP > "); 17
scanf("%d",&OrderNumber);
RowCounter = 0;
if (OrderNumber != 0) {
BeginTransaction(); 18
if (OpenCursor()) { 19
DoFetch = TRUE;
do {
printf("\n");
printf("\n FETCH the next row.");
EXEC SQL FETCH OrderReview 21
INTO :OrderNumber,
:ItemNumber,
:VendPartNumber,
:ReceivedQty :ReceivedQtyInd;
switch(sqlca.sqlcode) {
case OK: DisplayUpdate(); 22
break;
case NotFound: DoFetch = FALSE; 20
printf("\n");
printf("\n Row not found or no more rows!");
if (RowCounter > 0) {
printf("\n");
printf("\n Do you want to save your changes (Y/N)?>");
scanf("%s",response);
if ((response[0] == 'N') || (response[0] == 'n')) {
CloseCursor(); 9
RollBack();
}
else {
CloseCursor(); 9
EndTransaction(); 23
printf(RowCounter,"%d\n rows were changed!");
}
}
if (RowCounter == 0) {
CloseCursor(); 9
EndTransaction(); 23
}
break;
default: DoFetch = FALSE; 20
SQLStatusCheck();
CloseCursor(); 9
RollBack(); 24
break;
} /* End switch */
} while (DoFetch != FALSE); /* End do */
} /* End if open */
} /* End if OrderNumber */
} /* End of FetchUpdate Function */
main() /* Beginning of program */
{
printf("\n Program to UPDATE the OrderItems table via a CURSOR - cex8");
printf("\n");
printf("\n Event list:");
printf("\n CONNECT TO PartsDBE");
printf("\n Prompt for an Order Number");
printf("\n BEGIN WORK");
printf("\n OPEN CURSOR");
printf("\n FETCH a row");
printf("\n Display the retrieved row");
printf("\n Prompt for new Received Quantity");
printf("\n UPDATE row within the OrderItems table");
printf("\n FETCH the next row, if any, with the same Order Number");
printf("\n Repeat the above five steps until there are no more rows");
printf("\n CLOSE CURSOR");
printf("\n End Transaction");
printf("\n Repeat the above eleven steps until the user enters a 0");
printf("\n RELEASE the DBEnvironment");
printf("\n");
if (ConnectDBE()) { 27
DeclareCursor(); 26
Done = FALSE;
do {
FetchUpdate(); 28
printf("\n Do you want to FETCH another OrderNumber (Y/N)?>");
scanf("%s",response);
if ((response[0] == 'N') || (response[0] == 'n')) Done = TRUE;
} while (Done != TRUE);
ReleaseDBE(); 29
}
else
printf("\n Error: Cannot Connect to PartsDBE!\n");
} /* End of Program */
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