add nulls first/last support to order by expression (#176)

Following `<sort specification list>` from the standard https://jakewheat.github.io/sql-overview/sql-2016-foundation-grammar.html#_10_10_sort_specification_list

CHANGELOG.md

@@ -13,11 +13,13 @@ Check https://github.com/andygrove/sqlparser-rs/commits/master for undocumented
 - Support Snowflake's `FROM (table_name)` (#155) - thanks @eyalleshem!
 
 ### Added
-- Support basic forms of `CREATE INDEX` and `DROP INDEX` (#167) - thanks @mashuai!
-- Support `ON { UPDATE | DELETE } { RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT }` in `FOREIGN KEY` constraints (#170) - thanks @c7hm4r!
 - Support MSSQL `TOP (<N>) [ PERCENT ] [ WITH TIES ]` (#150) - thanks @alexkyllo!
 - Support MySQL `LIMIT row_count OFFSET offset` (not followed by `ROW` or `ROWS`) and remember which variant was parsed (#158) - thanks @mjibson!
 - Support PostgreSQL `CREATE TABLE IF NOT EXISTS table_name` (#163) - thanks @alex-dukhno!
+- Support basic forms of `CREATE INDEX` and `DROP INDEX` (#167) - thanks @mashuai!
+- Support `ON { UPDATE | DELETE } { RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT }` in `FOREIGN KEY` constraints (#170) - thanks @c7hm4r!
+- Support basic forms of `CREATE SCHEMA` and `DROP SCHEMA` (#173) - thanks @alex-dukhno!
+- Support `NULLS FIRST`/`LAST` in `ORDER BY` expressions (#176) - thanks @houqp!
 
 ### Fixed
 - Report an error for unterminated string literals (#165)

src/ast/query.rs

@@ -374,20 +374,30 @@ pub enum JoinConstraint {
     Natural,
 }
 
-/// SQL ORDER BY expression
+/// An `ORDER BY` expression
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct OrderByExpr {
     pub expr: Expr,
+    /// Optional `ASC` or `DESC`
     pub asc: Option<bool>,
+    /// Optional `NULLS FIRST` or `NULLS LAST`
+    pub nulls_first: Option<bool>,
 }
 
 impl fmt::Display for OrderByExpr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.expr)?;
         match self.asc {
-            Some(true) => write!(f, "{} ASC", self.expr),
-            Some(false) => write!(f, "{} DESC", self.expr),
-            None => write!(f, "{}", self.expr),
+            Some(true) => write!(f, " ASC")?,
+            Some(false) => write!(f, " DESC")?,
+            None => (),
         }
+        match self.nulls_first {
+            Some(true) => write!(f, " NULLS FIRST")?,
+            Some(false) => write!(f, " NULLS LAST")?,
+            None => (),
+        }
+        Ok(())
     }
 }
 

src/dialect/keywords.rs

@@ -220,6 +220,7 @@ define_keywords!(
     LAG,
     LANGUAGE,
     LARGE,
+    LAST,
     LAST_VALUE,
     LATERAL,
     LEAD,
@@ -262,6 +263,7 @@ define_keywords!(
     NTILE,
     NULL,
     NULLIF,
+    NULLS,
     NUMERIC,
     OBJECT,
     OCTET_LENGTH,

src/parser.rs

@@ -2015,7 +2015,20 @@ impl Parser {
         } else {
             None
         };
-        Ok(OrderByExpr { expr, asc })
+
+        let nulls_first = if self.parse_keywords(vec!["NULLS", "FIRST"]) {
+            Some(true)
+        } else if self.parse_keywords(vec!["NULLS", "LAST"]) {
+            Some(false)
+        } else {
+            None
+        };
+
+        Ok(OrderByExpr {
+            expr,
+            asc,
+            nulls_first,
+        })
     }
 
     /// Parse a TOP clause, MSSQL equivalent of LIMIT,

tests/sqlparser_common.rs

@@ -746,14 +746,17 @@ fn parse_select_order_by() {
                 OrderByExpr {
                     expr: Expr::Identifier(Ident::new("lname")),
                     asc: Some(true),
+                    nulls_first: None,
                 },
                 OrderByExpr {
                     expr: Expr::Identifier(Ident::new("fname")),
                     asc: Some(false),
+                    nulls_first: None,
                 },
                 OrderByExpr {
                     expr: Expr::Identifier(Ident::new("id")),
                     asc: None,
+                    nulls_first: None,
                 },
             ],
             select.order_by
@@ -775,10 +778,35 @@ fn parse_select_order_by_limit() {
             OrderByExpr {
                 expr: Expr::Identifier(Ident::new("lname")),
                 asc: Some(true),
+                nulls_first: None,
             },
             OrderByExpr {
                 expr: Expr::Identifier(Ident::new("fname")),
                 asc: Some(false),
+                nulls_first: None,
+            },
+        ],
+        select.order_by
+    );
+    assert_eq!(Some(Expr::Value(number("2"))), select.limit);
+}
+
+#[test]
+fn parse_select_order_by_nulls_order() {
+    let sql = "SELECT id, fname, lname FROM customer WHERE id < 5 \
+               ORDER BY lname ASC NULLS FIRST, fname DESC NULLS LAST LIMIT 2";
+    let select = verified_query(sql);
+    assert_eq!(
+        vec![
+            OrderByExpr {
+                expr: Expr::Identifier(Ident::new("lname")),
+                asc: Some(true),
+                nulls_first: Some(true),
+            },
+            OrderByExpr {
+                expr: Expr::Identifier(Ident::new("fname")),
+                asc: Some(false),
+                nulls_first: Some(false),
             },
         ],
         select.order_by
@@ -1251,7 +1279,8 @@ fn parse_window_functions() {
                 partition_by: vec![],
                 order_by: vec![OrderByExpr {
                     expr: Expr::Identifier(Ident::new("dt")),
-                    asc: Some(false)
+                    asc: Some(false),
+                    nulls_first: None,
                 }],
                 window_frame: None,
             }),