On Wed, Jan 10, 2024 at 1:49 PM ddme <ret2d...@qq.com> wrote: > > Hi all, > > I notice that the CREATE TYPE syntax can specify subtype_diff function > > CREATE TYPE name AS RANGE ( > SUBTYPE = subtype > [ , SUBTYPE_OPCLASS = subtype_operator_class ] > [ , COLLATION = collation ] > [ , CANONICAL = canonical_function ] > [ , SUBTYPE_DIFF = subtype_diff_function ] <————— here > [ , MULTIRANGE_TYPE_NAME = multirange_type_name ] > ) > > And a example is > ```sql > > CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi); > > ``` > > I notice that float8mi is a C function, and I find the call_subtype_diff() in > source code that it seems only can call C function.
call_subtype_diff() invokes FunctionCall2Coll() which in turn invokes the function handler for non-C functions. See fmgr_info_cxt_security() for example. So subtype_diff can be a SQL callable function written in any supported language. > > I want to know > > 1. Can the subtype_diff function in CREATE TYPE be sql or plpgsql function? I think so. > 2. How to call subtype_diff function? I know it related with GiST index, I > need a example on how to trigger subtype_diff function. I am not familiar with GiST code enough to answer that question. But looking at the places where call_subtype_diff() is called, esp. the comments there might give you hints. OR somebody more familiar with GiST code will give you a direct answer. -- Best Wishes, Ashutosh Bapat
