Redshift: Support APPROXIMATE PERCENTILE_DISC

src/dialect/redshift.rs

@@ -15,8 +15,14 @@
 // specific language governing permissions and limitations
 // under the License.
 
+#[cfg(not(feature = "std"))]
+use alloc::boxed::Box;
+
+use crate::ast::Expr;
 use crate::dialect::Dialect;
 use crate::keywords::Keyword;
+use crate::parser::{Parser, ParserError};
+use crate::tokenizer::Token;
 use core::iter::Peekable;
 use core::str::Chars;
 
@@ -35,6 +41,28 @@ pub struct RedshiftSqlDialect {}
 // in the Postgres dialect, the query will be parsed as an array, while in the Redshift dialect it will
 // be a json path
 impl Dialect for RedshiftSqlDialect {
+    fn parse_prefix(&self, parser: &mut Parser) -> Option<Result<Expr, ParserError>> {
+        if matches!(&parser.peek_token_ref().token, Token::Word(word) if word.value.eq_ignore_ascii_case("approximate"))
+            && matches!(&parser.peek_nth_token_ref(1).token, Token::Word(word) if word.value.eq_ignore_ascii_case("percentile_disc"))
+        {
+            parser.next_token();
+            let function_name = match parser.parse_object_name(false) {
+                Ok(name) => name,
+                Err(error) => return Some(Err(error)),
+            };
+            return Some(
+                parser
+                    .parse_function(function_name)
+                    .map(|function| Expr::Prefixed {
+                        prefix: "APPROXIMATE".into(),
+                        value: Box::new(function),
+                    }),
+            );
+        }
+
+        None
+    }
+
     /// Determine if a character starts a potential nested quoted identifier.
     /// Example: RedShift supports the following quote styles to all mean the same thing:
     /// ```sql

tests/sqlparser_redshift.rs

@@ -557,3 +557,17 @@ 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() {
+    redshift().one_statement_parses_to(
+        r#"SELECT TOP 10 date.caldate,
+COUNT(totalprice), SUM(totalprice),
+APPROXIMATE PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY totalprice)
+FROM listing
+JOIN date ON listing.dateid = date.dateid
+GROUP BY date.caldate
+ORDER BY 3 DESC"#,
+        "SELECT TOP 10 date.caldate, COUNT(totalprice), SUM(totalprice), APPROXIMATE PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY totalprice) FROM listing JOIN date ON listing.dateid = date.dateid GROUP BY date.caldate ORDER BY 3 DESC",
+    );
+}