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Thread: Decimal values in

Decimal values in

From
Masterprojekt Naumann1
Date:
Dear Dev-List,

inside execProcnode.c's ExecProcNode method we want to extract the value of a tuple for a specific attribute. This works great for integers and strings, but we are not able to figure out how to do this for floating point numbers. Below is some example code snippet to show our problem:

TupleTableSlot *
ExecProcNode(PlanState *node) {
TupleTableSlot *result;
        ...
        bool isNull;
        Datum datum = slot_getattr(result,0, &isNull);

        Form_pg_attribute *attrList = result->tts_tupleDescriptor->attrs;

        if(attrList[0]->atttypid==INT4OID){
                int value = (int) (datum);
                ...
        } else if(attrList[0]->atttypid==VARCHAROID){
                char* value = TextDatumGetCString(datum);
                ...
        //this does not work :(
        } else if(attrList[0]->atttypid==<DECIMAL_OID> /*what is the right OID*/){
                //the value does not seem to be stored in the datum
                float value = (float) (datum);
                ...
        }
        ...
}

How can we get those values?

Yours sincerely, Fabian Tschirschnitz.

Re: Decimal values in

From
Alvaro Herrera
Date:
Masterprojekt Naumann1 escribió:
> Dear Dev-List,
> 
> inside execProcnode.c's ExecProcNode method we want to extract the value of
> a tuple for a specific attribute. This works great for integers and
> strings, but we are not able to figure out how to do this for floating
> point numbers. Below is some example code snippet to show our problem:

"DECIMAL_OID" (you probably mean NUMERICOID) points to datatype numeric,
which is not floating point but a variable length datatype with its own
special encoding for storage.  If you want floating point you need
FLOAT4OID and FLOAT8OID, and columns created with types float and
"double precision", respectively.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

Re: Decimal values in

From
Tom Lane
Date:
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Masterprojekt Naumann1 escribi�:
>> inside execProcnode.c's ExecProcNode method we want to extract the value of
>> a tuple for a specific attribute. This works great for integers and
>> strings, but we are not able to figure out how to do this for floating
>> point numbers. Below is some example code snippet to show our problem:

> "DECIMAL_OID" (you probably mean NUMERICOID) points to datatype numeric,
> which is not floating point but a variable length datatype with its own
> special encoding for storage.  If you want floating point you need
> FLOAT4OID and FLOAT8OID, and columns created with types float and
> "double precision", respectively.

Also, you should not be using casts, but the appropriate DatumGetXXX
macro.  In some cases those reduce to a cast, but your code ought not
assume that.
        regards, tom lane