enh(query): add selectivity support for csum functions

TD-18050

source/libs/function/src/builtins.c

@@ -2487,7 +2487,7 @@ const SBuiltinFuncDefinition funcMgtBuiltins[] = {
   {
     .name = "csum",
     .type = FUNCTION_TYPE_CSUM,
-    .classification = FUNC_MGT_INDEFINITE_ROWS_FUNC | FUNC_MGT_TIMELINE_FUNC | FUNC_MGT_FORBID_STREAM_FUNC | FUNC_MGT_CUMULATIVE_FUNC,
+    .classification = FUNC_MGT_INDEFINITE_ROWS_FUNC | FUNC_MGT_SELECT_FUNC | FUNC_MGT_TIMELINE_FUNC | FUNC_MGT_FORBID_STREAM_FUNC | FUNC_MGT_CUMULATIVE_FUNC,
     .translateFunc = translateCsum,
     .getEnvFunc   = getCsumFuncEnv,
     .initFunc     = functionSetup,

source/libs/function/src/builtinsimpl.c

@@ -4781,6 +4781,11 @@ int32_t csumFunction(SqlFunctionCtx* pCtx) {
       }
     }
 
+    // handle selectivity
+    if (pCtx->subsidiaries.num > 0) {
+      appendSelectivityValue(pCtx, i, pos);
+    }
+
     numOfElems++;
   }