Re: How to convert a double value to a numeric datum type in pgsql?

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От Pavel Stehule
Тема Re: How to convert a double value to a numeric datum type in pgsql?
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Msg-id CAFj8pRBTnxdEx+DtWeEq6JGuJVgpUb0KJYfm81=Zz4Bu_L6frA@mail.gmail.com
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Ответ на How to convert a double value to a numeric datum type in pgsql?  (Felix.徐 <ygnhzeus@gmail.com>)
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hello

you have to look to postgresql/src/backend/utils/adt/numeric.c functions -

then you can call float8_numeric

Numeric result = DatumGetNumeric(DirectFunctionCall1(float8_numeric, Float8GetDatum(dx));

regards

Pavel


2014-02-24 7:45 GMT+01:00 Felix.徐 <ygnhzeus@gmail.com>:
Hi all,
I'm talking about the source code of pgsql and I want to know how the typing system works in pgsql.
A few functions can help us do the type conversion, for example:

Int32GetDatum -- convert a integer to a datum
Float8GetDatum -- convert double to a datum
cstring_to_text -- convert a string to a text
...

but there are a lot of types in pgsql,how to choose the corresponding function? or is there a more automatic way to do the type conversion(raw chars to a datum, suppose I have the corresponding Form_pg_type instance)?

I ask this question because I don't know how to convert a double value to a numeric datum(the field's type is numeric(10,2)), pg_type shows that numeric's typlen is -1 whose length is variable thus Float8GetDatum is not working..





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