return nil, errIncorrectSQLFunctionArgumentType(err)
	}

	// Assemble other arguments
	arg2, arg3 := e.From, e.For
	// Check if the second form of substring is being used
	if e.From == nil {
		arg2, arg3 = e.Arg2, e.Arg3
	}

	// Evaluate the FROM argument
	v2, err := arg2.evalNode(r, tableAlias)
	if err != nil {
		return nil, err
	}
	inferTypeForArithOp(v2)

type SubstringFunc struct {
	Expr *PrimaryTerm `parser:" \"SUBSTRING\" \"(\" @@ "`
	From *Operand     `parser:" ( \"FROM\" @@ "`
	For  *Operand     `parser:"   (\"FOR\" @@)? \")\" "`
	Arg2 *Operand     `parser:" | \",\" @@ "`
	Arg3 *Operand     `parser:"   (\",\" @@)? \")\" )"`
}

// ExtractFunc represents EXTRACT sql function
type ExtractFunc struct {

//
//	// schema has a "k0" relation and a "k7.k8" embedded relation
//	parsePreloadMap(schema, map[string][]interface{}{
//		clause.Associations: {"arg1"},
//		"k1":                {"arg2"},
//		"k2.k3":             {"arg3"},
//		"k4.k5.k6":          {"arg4"},
//	})
//	// preloadMap is
//	map[string]map[string][]interface{}{
//		"k0": {},
//		"k7": {
//			"k8": {},
//		},
//		"k1": {},

	//export MyFunction
	func MyFunction(arg1, arg2 int, arg3 string) int64 {...}

	//export MyFunction2
	func MyFunction2(arg1, arg2 int, arg3 string) (int64, *C.char) {...}

They will be available in the C code as:

	extern GoInt64 MyFunction(int arg1, int arg2, GoString arg3);
	extern struct MyFunction2_return MyFunction2(int arg1, int arg2, GoString arg3);

	ReplicationStatusInternal string                 // stringified representation of all replication activity
	// VersionPurgeStatusInternal is internally in the format "arn1=PENDING;arn2=COMPLETED;"
	VersionPurgeStatusInternal string                            // stringified representation of all version purge statuses