The following programs demonstrate the use of the REQUEST_HANDLE clause in a FOR statement. These programs: o Declare the variable, REQ1, for a request handle and the local variable, "name" o Initialize REQ1 to zero o Assign a value to "name" o Start a transaction o Use the request handle in the first FOR statement o Assign a new value to "name" o Use the same request handle again in the second FOR statement By using the same request handle in the second (identical) request the program can reuse the code generated in the first FOR statement for the second FOR statement; this enhances overall performance.
1 – C Example
#include <stdio.h> DATABASE PERS = FILENAME "PERSONNEL"; DECLARE_VARIABLE name SAME AS PERS.EMPLOYEES.LAST_NAME; extern long RDB$RELEASE_REQUEST(); RDML$HANDLE_TYPE REQ1; main() { REQ1 = 0; strcpy(name,"Gray"); READY PERS; START_TRANSACTION READ_ONLY; FOR (REQUEST_HANDLE REQ1) E IN PERS.EMPLOYEES WITH E.LAST_NAME = name printf("%s\n",E.FIRST_NAME); END_FOR; if ((RDB$RELEASE_REQUEST(RDB$MESSAGE_VECTOR, &REQ1) & 1) == 0) RDML$SIGNAL_ERROR(RDB$MESSAGE_VECTOR); COMMIT; FINISH; }
2 – Pascal Example
program request (input,output); DATABASE PERS = FILENAME 'PERSONNEL'; DECLARE_VARIABLE OF name SAME AS PERS.EMPLOYEES.LAST_NAME; REQ1 : RDML$HANDLE_TYPE; begin REQ1 := 0; name := 'Gray'; READY PERS; START_TRANSACTION READ_ONLY; FOR (REQUEST_HANDLE REQ1) E IN PERS.EMPLOYEES WITH E.LAST_NAME = name writeln (E.FIRST_NAME); END_FOR; if not RDB$RELEASE_REQUEST(RDB$MESSAGE_VECTOR, REQ1) then RDML$SIGNAL_ERROR(RDB$MESSAGE_VECTOR); COMMIT; FINISH; end.