Dynamic SQL with cursor variables in pro*c

Question

Please, what I need to do in order to be able
to do something like this:
EXEC SQL DECLARE :c CURSOR FOR :s;
In other words: I want to use variables
in cursor names.
Is it possible ? How ?
Thank you.

Answer 1

OK. Here is an example of a Dynamic SQL #4 program I wrote several years ago (It's still running in production). It is currently running on a Sun E10K with Oracle 8.1.5. This code is JUST the pro*c part of a program which uses IBM MQ Series. MQ passes this program a Select SQL statement (as well as other parameters) as an argument. The Pro*c code allocates the structures, parses, and fetches, and executes the statement. I realize that this will not be easy to read. There are SOME comments in the code. However, I realize that to read anyone elses code is a chore. When you add Dynamic #4 to the list, it becomes much more complicated. Anyway, you'll probably need to copy and paste the code to a text file. It will be easier to read.
==========================================
Code
==========================================
| Program: mqsql.pc |
| Creator: Jim Wartnick |
| Purpose: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX |
| XXXXXXXXXXX |
| Date: 01/03/1997 |
| Modifications: |
#include"mqsql.h"
#define DEBUG
#ifdef DEBUG
FILE *fp=stdout;
#endif
int
disconnect_db() {
char msg[256], oraclmsg[256];
char buf[MAX_STRING_LENGTH+4];
int buf_len = 0, msg_len = 0;
EXEC SQL
COMMIT WORK RELEASE;
#ifdef DEBUG
fprintf(fp, " --> Disconnecting from database. RC: %d.\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
error("disconnect_db()", "disconnect", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
connect_db() {
char msg[256], oraclmsg[256];
char buf[MAX_STRING_LENGTH+4];
int buf_len = 0, msg_len = 0;
char user[4];
strcpy(user, "/");
EXEC SQL
CONNECT :user;
#ifdef DEBUG
fprintf(fp, " --> Connecting to database. RC is %d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
sprintf(Results, "%9d", sqlca.sqlcode);
error("connect_db()", "connect", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
allocate_sqlda() {
| Initialize the SQLDA structure. |
| We only need the select descriptor |
| because we do not have any bind |
| variables. |
if ((Select_da = sqlald(
MAX_COLUMN_COUNT,
MAX_COLUMN_STRING_LENGTH,
MAX_INDICATOR_VARS
)) == (SQLDA *) 0) {
#ifdef DEBUG
fprintf(fp, " Memory allocation for Select Descriptor failed.\n");
fflush(fp);
#endif
strcpy(Results, "000000001");
error("allocate_sqlda()", "create SQLDA", 0, "Memory Error");
return(FAILURE);
#ifdef DEBUG
fprintf(fp, " Memory allocation for Select Descriptor succeeded.\n");
fflush(fp);
#endif
Select_da->N = MAX_COLUMN_COUNT;
return(SUCCESS);
int
prepare_sql() {
char msg[256], oraclmsg[256];
int buf_len = 0, msg_len = 0;
| Prepare the Sql statement. |
EXEC SQL
PREPARE sql_stmt
FROM :Sql;
#ifdef DEBUG
fprintf(fp, " Prepared SQL: %s. RC: %d.\n", Sql, sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
sprintf(Results, "%9d", sqlca.sqlcode);
error("prepare_sql()", "Parse", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
declare_cursor() {
char msg[256], oraclmsg[256];
int buf_len = 0, msg_len = 0;
| Set up the cursor to loop through |
EXEC SQL
DECLARE sql_cursor
CURSOR FOR sql_stmt;
#ifdef DEBUG
fprintf(fp, " Declared cursor. RC: %d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof( oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
sprintf(Results, "%9d", sqlca.sqlcode);
error("declare_cursor()", "declare cursor", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
open_cursor() {
char msg[256], oraclmsg[256];
int buf_len = 0, msg_len = 0;
| Open the cursor. |
EXEC SQL
OPEN sql_cursor;
#ifdef DEBUG
fprintf(fp, " Opened cursor. RC:%d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
sprintf(Results, "%9d", sqlca.sqlcode);
error("open_cursor()", "open cursor", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
describe_select_list() {
char msg[256], oraclmsg[256];
int buf_len = 0, msg_len = 0;
| Get description of columns |
EXEC SQL
DESCRIBE SELECT LIST FOR sql_stmt
INTO Select_da;
#ifdef DEBUG
fprintf(fp, " Described columns. RC %d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
sprintf(Results, "%9d", sqlca.sqlcode);
error("describe_select_list()", "describe select list", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
setup_sqlda() {
char buf[MAX_STRING_LENGTH+4];
int done = FALSE, nullok = 0, i = 0;
#ifdef DEBUG
fprintf(fp, " --> Setting up SQLDA.\n");
fflush(fp);
#endif
if (allocate_sqlda() == FAILURE)
return(FAILURE);
if (prepare_sql() == FAILURE)
return(FAILURE);
if (declare_cursor() == FAILURE)
return(FAILURE);
if (open_cursor() == FAILURE)
return(FAILURE);
if (describe_select_list() == FAILURE)
return(FAILURE);
| Too many columns in select list. |
if (Select_da->F < 0) {
strcpy(Results, "000000001");
error("setup_sqlda()", "check select list count", 0, "Too many values in select list");
return(FAILURE);
| Set the number of columns to the actual |
| number of columns. |
Select_da->N = Select_da->F;
| We are going to convert all fields to a string. |
for (i == 0; i < Select_da->F; i++) {
sqlnul(&(Select_da->T), &(Select_da->T[i]), &nullok);
Select_da->T[i] = EXT_STRING;
Select_da->L[i] = MAX_STRING_LENGTH;
| Allocate the result area to be as big as |
| MAX_STRING_LENGTH. |
if ((Select_da->V[i] = malloc(Select_da->L[i])) == NULL) {
#ifdef DEBUG
fprintf(fp, " Allocation of column values failed.\n");
fflush(fp);
#endif
strcpy(Results, "000000001");
error("setup_sqlda()", "allocate column values", 0, "Memory Error");
return(FAILURE);
if ((Select_da->I[i] = (short *) malloc(sizeof(short))) == NULL) {
#ifdef DEBUG
fprintf(fp, " Allocation of idicator values failed.\n");
fflush(fp);
#endif
strcpy(Results, "000000001");
error("setup_sqlda()", "allocate indicator values", 0, "Memory Error");
return(FAILURE);
#ifdef DEBUG
fprintf(fp, " Allocation of memory for values succeeded.\n");
fflush(fp);
#endif
return(SUCCESS);
| add_eom adds the end of message |
| delimiter (an aditional comma). |
int
add_eom() {
char *result_ptr;
if (strlen(Results) >= sizeof(Results) - 1) {
strcpy(Results, "000000001");
error("add_eom()", "Add eom failed. Size overflow", 0, "Memory Error");
return(FAILURE);
result_ptr = &Results[strlen(Results)-1];
while (*result_ptr && (*result_ptr != ','))
result_ptr--;
if (*result_ptr) {
result_ptr++;
*(result_ptr++) = ',';
*result_ptr = '\0';
return(SUCCESS);
int close_cursor() {
char msg[256], oraclmsg[256];
int buf_len = 0, msg_len = 0;
| Close the cursor. |
EXEC SQL
CLOSE sql_cursor;
#ifdef DEBUG
fprintf(fp, " Closing cursor. RC: %d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
error("generate_sql()", "close cursor", sqlca.sqlcode, oraclmsg);
return(FAILURE);
return(SUCCESS);
int
fetch() {
char msg[256], oraclmsg[256];
char buf[MAX_STRING_LENGTH+4];
int buf_len = 0, msg_len = 0;
EXEC SQL
FETCH sql_cursor
USING DESCRIPTOR Select_da;
#ifdef DEBUG
fprintf(fp, " --> Fetching rows. RC %d\n", sqlca.sqlcode);
fflush(fp);
#endif
if (sqlca.sqlcode != 0) {
if (sqlca.sqlcode != NODATAFOUND) {
buf_len = sizeof(oraclmsg)-1;
sqlglm(oraclmsg, &buf_len, &msg_len);
oraclmsg[msg_len] = '\0';
error("fetch()", "Error fetching row.", sqlca.sqlcode, oraclmsg);
return(sqlca.sqlcode);
return(NODATAFOUND);
return(SUCCESS);
| Free up any memory structures. |
void
free_memory() {
int i = 0;
for (i = 0; i < Select_da->F; i++) {
free(Select_da->V[i]);
free(Select_da->I[i]);
| generate_sql() uses the message we received from the queue |
| (a SQL statement) to query the database. We have to use |
| dynamic Sql Version 4 for this type of Sql. The number of |
| columns we are selecting is unknown. This means we can't |
| use the INTO clause. |
int
generate_sql() {
char buf[MAX_STRING_LENGTH+4];
int rc = SUCCESS, done = FALSE, nullok = 0, i = 0;
#ifdef DEBUG
if ((fp = fopen(SQLLOG, "a")) == NULL)
fp = stderr;
#endif
| Connect to the database |
if (connect_db() == FAILURE)
return(FAILURE);
if (setup_sqlda() == FAILURE)
return(FAILURE);
| Place the answer in a comma delimited buffer. |
memset(Results, NULL, sizeof(Results));
done = FALSE;
while (!done) {
rc = fetch();
if (rc != SUCCESS) {
if (Results[0] == '\0')
sprintf(Results, "%9d,", rc);
done = TRUE;
else {
| Put return code of success in first. |
if (Results[0] == '\0')
strcpy(Results, "000000000,");
for (i = 0; i < Select_da->F; i++) {
Select_da->V[i][Select_da->L[i]] = '\0';
| Check to see if the value is null. |
if (*Select_da->I[i] < 0)
strcpy(buf, " ,");
else
sprintf(buf, "%s,", Select_da->V[i]);
if (strlen(Results) + strlen(buf) > sizeof(Results)) {
strcpy(Results, "000000001");
error("generate_sql()", "String concat failed. Size overflow", 0, "Memory Error");
return(FAILURE);
strcat(Results, buf);
#ifdef DEBUG
fprintf(fp, " --> Results %s\n", Results);
fflush(fp);
#endif
| Close the cursor. |
close_cursor();
| Disconnect from the database |
disconnect_db();
| Remove trailing comma. |
if (add_eom() == FAILURE)
return(FAILURE);
#ifdef DEBUG
fflush(fp);
#endif
free_memory();
#ifdef DEBUG
fclose(fp);
#endif
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