@@ -7175,6 +7175,8 @@ impl Spanned for AlterOperatorClass {
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
 pub struct AlterFunction {
+    /// Whether an absent function is ignored.
+    pub if_exists: bool,
     /// Object type being altered.
     pub kind: AlterFunctionKind,
     /// Function or aggregate signature.
@@ -7285,6 +7287,9 @@ pub enum AlterFunctionAction {
 impl fmt::Display for AlterFunction {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "ALTER {} ", self.kind)?;
+        if self.if_exists {
+            write!(f, "IF EXISTS ")?;
+        }
         match self.kind {
             AlterFunctionKind::Function => {
                 write!(f, "{} ", self.function)?;
 
@@ -13519,6 +13519,7 @@ impl<'a> Parser<'a> {
         &mut self,
         kind: AlterFunctionKind,
     ) -> Result<Statement, ParserError> {
+        let if_exists = self.parse_keywords(&[Keyword::IF, Keyword::EXISTS]);
         let (function, aggregate_star, aggregate_order_by) = match kind {
             AlterFunctionKind::Function => (self.parse_function_desc()?, false, None),
             AlterFunctionKind::Aggregate => self.parse_alter_aggregate_signature()?,
@@ -13569,6 +13570,7 @@ impl<'a> Parser<'a> {
         };
 
         Ok(Statement::AlterFunction(AlterFunction {
+            if_exists,
             kind,
             function,
             aggregate_order_by,