Support trailing commas in FROM clause (#1645)

Co-authored-by: Ifeanyi Ubah <ify1992@yahoo.com>

src/dialect/mod.rs

@@ -404,6 +404,12 @@ pub trait Dialect: Debug + Any {
         self.supports_trailing_commas()
     }
 
+    /// Returns true if the dialect supports trailing commas in the `FROM` clause of a `SELECT` statement.
+    /// /// Example: `SELECT 1 FROM T, U, LIMIT 1`
+    fn supports_from_trailing_commas(&self) -> bool {
+        false
+    }
+
     /// Returns true if the dialect supports double dot notation for object names
     ///
     /// Example
@@ -775,6 +781,12 @@ pub trait Dialect: Debug + Any {
         keywords::RESERVED_FOR_IDENTIFIER.contains(&kw)
     }
 
+    // Returns reserved keywords when looking to parse a [TableFactor].
+    /// See [Self::supports_from_trailing_commas]
+    fn get_reserved_keywords_for_table_factor(&self) -> &[Keyword] {
+        keywords::RESERVED_FOR_TABLE_FACTOR
+    }
+
     /// Returns true if this dialect supports the `TABLESAMPLE` option
     /// before the table alias option. For example:
     ///

src/dialect/snowflake.rs

@@ -54,6 +54,10 @@ impl Dialect for SnowflakeDialect {
         true
     }
 
+    fn supports_from_trailing_commas(&self) -> bool {
+        true
+    }
+
     // Snowflake supports double-dot notation when the schema name is not specified
     // In this case the default PUBLIC schema is used
     //

src/keywords.rs

@@ -999,6 +999,16 @@ pub const RESERVED_FOR_COLUMN_ALIAS: &[Keyword] = &[
     Keyword::END,
 ];
 
+// Global list of reserved keywords alloweed after FROM.
+// Parser should call Dialect::get_reserved_keyword_after_from
+// to allow for each dialect to customize the list.
+pub const RESERVED_FOR_TABLE_FACTOR: &[Keyword] = &[
+    Keyword::INTO,
+    Keyword::LIMIT,
+    Keyword::HAVING,
+    Keyword::WHERE,
+];
+
 /// Global list of reserved keywords that cannot be parsed as identifiers
 /// without special handling like quoting. Parser should call `Dialect::is_reserved_for_identifier`
 /// to allow for each dialect to customize the list.

src/parser/mod.rs

@@ -3940,7 +3940,11 @@ impl<'a> Parser<'a> {
         let trailing_commas =
             self.options.trailing_commas | self.dialect.supports_projection_trailing_commas();
 
-        self.parse_comma_separated_with_trailing_commas(|p| p.parse_select_item(), trailing_commas)
+        self.parse_comma_separated_with_trailing_commas(
+            |p| p.parse_select_item(),
+            trailing_commas,
+            None,
+        )
     }
 
     pub fn parse_actions_list(&mut self) -> Result<Vec<ParsedAction>, ParserError> {
@@ -3966,20 +3970,32 @@ impl<'a> Parser<'a> {
         Ok(values)
     }
 
+    /// Parse a list of [TableWithJoins]
+    fn parse_table_with_joins(&mut self) -> Result<Vec<TableWithJoins>, ParserError> {
+        let trailing_commas = self.dialect.supports_from_trailing_commas();
+
+        self.parse_comma_separated_with_trailing_commas(
+            Parser::parse_table_and_joins,
+            trailing_commas,
+            Some(self.dialect.get_reserved_keywords_for_table_factor()),
+        )
+    }
+
     /// Parse the comma of a comma-separated syntax element.
     /// Allows for control over trailing commas
     /// Returns true if there is a next element
-    fn is_parse_comma_separated_end_with_trailing_commas(&mut self, trailing_commas: bool) -> bool {
+    fn is_parse_comma_separated_end_with_trailing_commas(
+        &mut self,
+        trailing_commas: bool,
+        reserved_keywords: Option<&[Keyword]>,
+    ) -> bool {
+        let reserved_keywords = reserved_keywords.unwrap_or(keywords::RESERVED_FOR_COLUMN_ALIAS);
         if !self.consume_token(&Token::Comma) {
             true
         } else if trailing_commas {
             let token = self.peek_token().token;
             match token {
-                Token::Word(ref kw)
-                    if keywords::RESERVED_FOR_COLUMN_ALIAS.contains(&kw.keyword) =>
-                {
-                    true
-                }
+                Token::Word(ref kw) if reserved_keywords.contains(&kw.keyword) => true,
                 Token::RParen | Token::SemiColon | Token::EOF | Token::RBracket | Token::RBrace => {
                     true
                 }
@@ -3993,7 +4009,7 @@ impl<'a> Parser<'a> {
     /// Parse the comma of a comma-separated syntax element.
     /// Returns true if there is a next element
     fn is_parse_comma_separated_end(&mut self) -> bool {
-        self.is_parse_comma_separated_end_with_trailing_commas(self.options.trailing_commas)
+        self.is_parse_comma_separated_end_with_trailing_commas(self.options.trailing_commas, None)
     }
 
     /// Parse a comma-separated list of 1+ items accepted by `F`
@@ -4001,7 +4017,7 @@ impl<'a> Parser<'a> {
     where
         F: FnMut(&mut Parser<'a>) -> Result<T, ParserError>,
     {
-        self.parse_comma_separated_with_trailing_commas(f, self.options.trailing_commas)
+        self.parse_comma_separated_with_trailing_commas(f, self.options.trailing_commas, None)
     }
 
     /// Parse a comma-separated list of 1+ items accepted by `F`
@@ -4010,6 +4026,7 @@ impl<'a> Parser<'a> {
         &mut self,
         mut f: F,
         trailing_commas: bool,
+        reserved_keywords: Option<&[Keyword]>,
     ) -> Result<Vec<T>, ParserError>
     where
         F: FnMut(&mut Parser<'a>) -> Result<T, ParserError>,
@@ -4017,7 +4034,10 @@ impl<'a> Parser<'a> {
         let mut values = vec![];
         loop {
             values.push(f(self)?);
-            if self.is_parse_comma_separated_end_with_trailing_commas(trailing_commas) {
+            if self.is_parse_comma_separated_end_with_trailing_commas(
+                trailing_commas,
+                reserved_keywords,
+            ) {
                 break;
             }
         }
@@ -10073,7 +10093,7 @@ impl<'a> Parser<'a> {
         // or `from`.
 
         let from = if self.parse_keyword(Keyword::FROM) {
-            self.parse_comma_separated(Parser::parse_table_and_joins)?
+            self.parse_table_with_joins()?
         } else {
             vec![]
         };

tests/sqlparser_common.rs

@@ -12957,8 +12957,38 @@ fn parse_update_from_before_select() {
         parse_sql_statements(query).unwrap_err()
     );
 }
-
 #[test]
 fn parse_overlaps() {
     verified_stmt("SELECT (DATE '2016-01-10', DATE '2016-02-01') OVERLAPS (DATE '2016-01-20', DATE '2016-02-10')");
 }
+
+#[test]
+fn test_trailing_commas_in_from() {
+    let dialects = all_dialects_where(|d| d.supports_from_trailing_commas());
+    dialects.verified_only_select_with_canonical("SELECT 1, 2 FROM t,", "SELECT 1, 2 FROM t");
+
+    dialects
+        .verified_only_select_with_canonical("SELECT 1, 2 FROM t1, t2,", "SELECT 1, 2 FROM t1, t2");
+
+    let sql = "SELECT a, FROM b, LIMIT 1";
+    let _ = dialects.parse_sql_statements(sql).unwrap();
+
+    let sql = "INSERT INTO a SELECT b FROM c,";
+    let _ = dialects.parse_sql_statements(sql).unwrap();
+
+    let sql = "SELECT a FROM b, HAVING COUNT(*) > 1";
+    let _ = dialects.parse_sql_statements(sql).unwrap();
+
+    let sql = "SELECT a FROM b, WHERE c = 1";
+    let _ = dialects.parse_sql_statements(sql).unwrap();
+
+    // nasted
+    let sql = "SELECT 1, 2 FROM (SELECT * FROM t,),";
+    let _ = dialects.parse_sql_statements(sql).unwrap();
+
+    // multiple_subqueries
+    dialects.verified_only_select_with_canonical(
+        "SELECT 1, 2 FROM (SELECT * FROM t1), (SELECT * FROM t2),",
+        "SELECT 1, 2 FROM (SELECT * FROM t1), (SELECT * FROM t2)",
+    );
+}