Redshift: Support APPROXIMATE PERCENTILE_DISC

src/dialect/mod.rs

@@ -598,6 +598,12 @@ pub trait Dialect: Debug + Any {
         None
     }
 
+    /// Does the dialect support the `APPROXIMATE PERCENTILE_DISC` function syntax?
+    /// See <https://docs.aws.amazon.com/redshift/latest/dg/r_APPROXIMATE_PERCENTILE_DISC.html>
+    fn supports_approximate_percentile_disc(&self) -> bool {
+        false
+    }
+
     /// Does the dialect support trailing commas around the query?
     fn supports_trailing_commas(&self) -> bool {
         false

src/dialect/redshift.rs

@@ -128,6 +128,11 @@ impl Dialect for RedshiftSqlDialect {
         true
     }
 
+    /// See <https://docs.aws.amazon.com/redshift/latest/dg/r_APPROXIMATE_PERCENTILE_DISC.html>
+    fn supports_approximate_percentile_disc(&self) -> bool {
+        true
+    }
+
     fn supports_geometric_types(&self) -> bool {
         true
     }

src/keywords.rs

@@ -121,6 +121,7 @@ define_keywords!(
     APPLICATION,
     APPLY,
     APPLYBUDGET,
+    APPROXIMATE,
     ARCHIVE,
     ARE,
     ARRAY,

src/parser/mod.rs

@@ -1635,6 +1635,18 @@ impl<'a> Parser<'a> {
             Keyword::MAP if *self.peek_token_ref() == Token::LBrace && self.dialect.support_map_literal_syntax() => {
                 Ok(Some(self.parse_duckdb_map_literal()?))
             }
+            Keyword::APPROXIMATE
+                if self.dialect.supports_approximate_percentile_disc()
+                    && self.peek_keyword(Keyword::PERCENTILE_DISC) =>
+            {
+                self.maybe_parse(|parser| {
+                    let function_name = parser.parse_object_name(false)?;
+                    parser.parse_function(function_name).map(|function| Expr::Prefixed {
+                        prefix: w.to_ident(w_span),
+                        value: Box::new(function),
+                    })
+                })
+            }
             Keyword::LAMBDA if self.dialect.supports_lambda_functions() => {
                 Ok(Some(self.parse_lambda_expr()?))
             }

tests/sqlparser_redshift.rs

@@ -557,3 +557,19 @@ fn parse_unpivot_expression() {
 fn test_interval_as_column_name() {
     redshift().verified_stmt("SELECT * FROM table_name WHERE interval = 78");
 }
+
+#[test]
+fn parse_approximate_percentile_disc() {
+    let supporting = all_dialects_where(|d| d.supports_approximate_percentile_disc());
+    supporting.verified_stmt(
+        "SELECT APPROXIMATE PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY totalprice)",
+    );
+
+    // Without dialect support, `APPROXIMATE` is just a column name and
+    // `PERCENTILE_DISC` its implicit alias.
+    let non_supporting = all_dialects_where(|d| !d.supports_approximate_percentile_disc());
+    non_supporting.one_statement_parses_to(
+        "SELECT APPROXIMATE PERCENTILE_DISC FROM t",
+        "SELECT APPROXIMATE AS PERCENTILE_DISC FROM t",
+    );
+}