Extract constants from EXECUTE queries - Mailing list pgsql-hackers

Hi hackers, I wanted to extract constants hard coded within prepared statements.

ex:-

PREPARE stmt(text, int) as SELECT * FROM test_table WHERE a = $1 AND b = 99 AND c = $2;

EXECUTE stmt('abc', 1);

I can easily get the parameter values ('abc' and 1) from queryDesc->params, but I need to also extract the constant value (99) from within the queryDesc structure during EXECUTE.


I've tried traversing the plan tree like this:

    List *constants = NIL;

    extract_constants_from_plan(queryDesc->plannedstmt->planTree, &constants);

    ListCell *lc;

    foreach(lc, constants)

    {

        Const *c = (Const *) lfirst(lc);

        if (!c->constisnull)

        {

            char *valueStr = NULL;

            switch (c->consttype)

            {

                case BOOLOID:

                    valueStr = DatumGetBool(c->constvalue) ? "true" : "false";

                    break;

                case INT2OID:

                    valueStr = psprintf("%d", DatumGetInt16(c->constvalue));

                    break;

                case INT4OID:

                    valueStr = psprintf("%d", DatumGetInt32(c->constvalue));

                    break;

                case INT8OID:

                    valueStr = psprintf("%ld", DatumGetInt64(c->constvalue));

                    break;

                case FLOAT4OID:

                    valueStr = psprintf("%f", DatumGetFloat4(c->constvalue));

                    break;

                case FLOAT8OID:

                    valueStr = psprintf("%f", DatumGetFloat8(c->constvalue));

                    break;

                case TEXTOID:

                case VARCHAROID:

                case BPCHAROID:

                    valueStr = TextDatumGetCString(c->constvalue);

                    break;

                default:

                    /* For unknown types, try to convert to string using output function */

                    valueStr = OidOutputFunctionCall(c->consttype, c->constvalue);

                    break;

            }

            FILE* fptr = fopen("/Users/abc/test.txt","a");

            fprintf(fptr, "Constant value: %s\n", valueStr);

            fclose(fptr);

        }

    }

But this does not seems to work for select statements, though this works for fine for prepared insert statements. Is there a general/ simpler way to do this?