diff --git a/src/binder/bind_expression/bind_comparison_expression.cpp b/src/binder/bind_expression/bind_comparison_expression.cpp
index 783c87600b4..413d76fd17e 100644
--- a/src/binder/bind_expression/bind_comparison_expression.cpp
+++ b/src/binder/bind_expression/bind_comparison_expression.cpp
@@ -77,7 +77,7 @@ std::shared_ptr<Expression> ExpressionBinder::bindComparisonExpression(
         // Resolve exec and select function if necessary
         // Only used for decimal at the moment. See `bindDecimalCompare`.
         function->bindFunc({childrenAfterCast, function, nullptr,
-            std::vector<std::string>{} /* optionalParams */});
+            binder::expression_vector{} /* optionalParams */});
     }
     auto bindData = std::make_unique<FunctionBindData>(LogicalType(function->returnTypeID));
     auto uniqueExpressionName =
diff --git a/src/binder/bind_expression/bind_function_expression.cpp b/src/binder/bind_expression/bind_function_expression.cpp
index 5e014e6f117..191d4dbe43b 100644
--- a/src/binder/bind_expression/bind_function_expression.cpp
+++ b/src/binder/bind_expression/bind_function_expression.cpp
@@ -1,5 +1,6 @@
 #include "binder/binder.h"
 #include "binder/expression/aggregate_function_expression.h"
+#include "binder/expression/expression.h"
 #include "binder/expression/scalar_function_expression.h"
 #include "binder/expression_binder.h"
 #include "catalog/catalog.h"
@@ -45,15 +46,17 @@ std::shared_ptr<Expression> ExpressionBinder::bindFunctionExpression(const Parse
 std::shared_ptr<Expression> ExpressionBinder::bindScalarFunctionExpression(
     const ParsedExpression& parsedExpression, const std::string& functionName) {
     expression_vector children;
+    expression_vector optionalParams;
     for (auto i = 0u; i < parsedExpression.getNumChildren(); ++i) {
         auto expr = bindExpression(*parsedExpression.getChild(i));
-        if (parsedExpression.getChild(i)->hasAlias()) {
+        if (!parsedExpression.getChild(i)->hasAlias()) {
+            children.push_back(expr);
+        } else {
             expr->setAlias(parsedExpression.getChild(i)->getAlias());
+            optionalParams.push_back(expr);
         }
-        children.push_back(expr);
     }
-    return bindScalarFunctionExpression(children, functionName,
-        parsedExpression.constCast<ParsedFunctionExpression>().getOptionalArguments());
+    return bindScalarFunctionExpression(children, functionName, optionalParams);
 }
 
 static std::vector<LogicalType> getTypes(const expression_vector& exprs) {
@@ -66,7 +69,7 @@ static std::vector<LogicalType> getTypes(const expression_vector& exprs) {
 
 std::shared_ptr<Expression> ExpressionBinder::bindScalarFunctionExpression(
     const expression_vector& children, const std::string& functionName,
-    std::vector<std::string> optionalArguments) {
+    binder::expression_vector optionalArguments) {
     auto catalog = Catalog::Get(*context);
     auto transaction = transaction::Transaction::Get(*context);
     auto childrenTypes = getTypes(children);
@@ -175,7 +178,7 @@ std::shared_ptr<Expression> ExpressionBinder::bindAggregateFunctionExpression(
     std::unique_ptr<FunctionBindData> bindData;
     if (function.bindFunc) {
         auto bindInput = ScalarBindFuncInput{children, &function, context,
-            std::vector<std::string>{} /* optionalParams */};
+            binder::expression_vector{} /* optionalParams */};
         bindData = function.bindFunc(bindInput);
     } else {
         bindData = std::make_unique<FunctionBindData>(LogicalType(function.returnTypeID));
diff --git a/src/function/struct/struct_pack_function.cpp b/src/function/struct/struct_pack_function.cpp
index 57576f32993..5ab5cc83cc2 100644
--- a/src/function/struct/struct_pack_function.cpp
+++ b/src/function/struct/struct_pack_function.cpp
@@ -23,7 +23,7 @@ static std::unique_ptr<FunctionBindData> bindFunc(const ScalarBindFuncInput& inp
             throw BinderException(
                 stringFormat("Cannot infer field name for {}.", argument->toString()));
         }
-        auto fieldName = input.optionalArguments[i];
+        auto fieldName = input.optionalArguments[i]->getAlias();
         if (fieldNameSet.contains(fieldName)) {
             throw BinderException(stringFormat("Found duplicate field {} in STRUCT.", fieldName));
         } else {
diff --git a/src/function/union/union_value_function.cpp b/src/function/union/union_value_function.cpp
index d98e2bfc111..fedb1ca8094 100644
--- a/src/function/union/union_value_function.cpp
+++ b/src/function/union/union_value_function.cpp
@@ -7,37 +7,35 @@ namespace kuzu {
 namespace function {
 
 static std::unique_ptr<FunctionBindData> bindFunc(const ScalarBindFuncInput& input) {
-    KU_ASSERT(input.arguments.size() == 1);
+    KU_ASSERT(input.optionalArguments.size() == 1);
     std::vector<StructField> fields;
-    if (input.arguments[0]->getDataType().getLogicalTypeID() == common::LogicalTypeID::ANY) {
-        input.arguments[0]->cast(LogicalType::STRING());
+    if (input.optionalArguments[0]->getDataType().getLogicalTypeID() ==
+        common::LogicalTypeID::ANY) {
+        input.optionalArguments[0]->cast(LogicalType::STRING());
     }
-    fields.emplace_back(input.arguments[0]->getAlias(), input.arguments[0]->getDataType().copy());
+    fields.emplace_back(input.optionalArguments[0]->getAlias(),
+        input.optionalArguments[0]->getDataType().copy());
     auto resultType = LogicalType::UNION(std::move(fields));
-    return FunctionBindData::getSimpleBindData(input.arguments, resultType);
+    return FunctionBindData::getSimpleBindData(input.optionalArguments, resultType);
 }
 
-static void execFunc(const std::vector<std::shared_ptr<common::ValueVector>>&,
+static void execFunc(const std::vector<std::shared_ptr<common::ValueVector>>& parameters,
     const std::vector<common::SelectionVector*>&, common::ValueVector& result,
     common::SelectionVector* resultSelVector, void* /*dataPtr*/) {
+    // (Tanvir) This is broken, parameters does not include optional params so we would
+    // get an out of bounds error
+    KU_ASSERT_UNCONDITIONAL(false);
+    result.setState(parameters[0]->state);
+    UnionVector::getTagVector(&result)->setState(parameters[0]->state);
+    UnionVector::referenceVector(&result, UnionType::TAG_FIELD_IDX, parameters[0]);
     UnionVector::setTagField(result, *resultSelVector, UnionType::TAG_FIELD_IDX);
 }
 
-static void valueCompileFunc(FunctionBindData* /*bindData*/,
-    const std::vector<std::shared_ptr<ValueVector>>& parameters,
-    std::shared_ptr<ValueVector>& result) {
-    KU_ASSERT(parameters.size() == 1);
-    result->setState(parameters[0]->state);
-    UnionVector::getTagVector(result.get())->setState(parameters[0]->state);
-    UnionVector::referenceVector(result.get(), UnionType::TAG_FIELD_IDX, parameters[0]);
-}
-
 function_set UnionValueFunction::getFunctionSet() {
     function_set functionSet;
-    auto function = std::make_unique<ScalarFunction>(name,
-        std::vector<LogicalTypeID>{LogicalTypeID::ANY}, LogicalTypeID::UNION, execFunc);
+    auto function = std::make_unique<ScalarFunction>(name, std::vector<LogicalTypeID>{},
+        LogicalTypeID::UNION, execFunc);
     function->bindFunc = bindFunc;
-    function->compileFunc = valueCompileFunc;
     functionSet.push_back(std::move(function));
     return functionSet;
 }
diff --git a/src/include/binder/expression_binder.h b/src/include/binder/expression_binder.h
index 5564d0c4da1..3816d0e2a95 100644
--- a/src/include/binder/expression_binder.h
+++ b/src/include/binder/expression_binder.h
@@ -86,7 +86,7 @@ class ExpressionBinder {
         const parser::ParsedExpression& parsedExpression, const std::string& functionName);
     std::shared_ptr<Expression> bindScalarFunctionExpression(const expression_vector& children,
         const std::string& functionName,
-        std::vector<std::string> optionalArguments = std::vector<std::string>{});
+        binder::expression_vector optionalArguments = binder::expression_vector{});
     std::shared_ptr<Expression> bindRewriteFunctionExpression(const parser::ParsedExpression& expr);
     std::shared_ptr<Expression> bindAggregateFunctionExpression(
         const parser::ParsedExpression& parsedExpression, const std::string& functionName,
diff --git a/src/include/function/function.h b/src/include/function/function.h
index 5559a78d4ef..aa43c2a9e4f 100644
--- a/src/include/function/function.h
+++ b/src/include/function/function.h
@@ -47,10 +47,10 @@ struct ScalarBindFuncInput {
     const binder::expression_vector& arguments;
     Function* definition;
     main::ClientContext* context;
-    std::vector<std::string> optionalArguments;
+    const binder::expression_vector optionalArguments;
 
     ScalarBindFuncInput(const binder::expression_vector& arguments, Function* definition,
-        main::ClientContext* context, std::vector<std::string> optionalArguments)
+        main::ClientContext* context, binder::expression_vector optionalArguments)
         : arguments{arguments}, definition{definition}, context{context},
           optionalArguments{std::move(optionalArguments)} {}
 };