Improve support for reserved keywords as table aliases in Snowflake

yoavcloud · yoavcloud · commit 61010ee4526e · 2025-07-09T16:23:34.000+02:00
diff --git a/src/dialect/mod.rs b/src/dialect/mod.rs
@@ -992,11 +992,17 @@ pub trait Dialect: Debug + Any {
         explicit || self.is_column_alias(kw, parser)
     }
 
+    /// Returns true if the specified keyword should be parsed as a table identifier.
+    /// See [keywords::RESERVED_FOR_TABLE_ALIAS]
+    fn is_table_alias(&self, kw: &Keyword, _parser: &mut Parser) -> bool {
+        !keywords::RESERVED_FOR_TABLE_ALIAS.contains(kw)
+    }
+
     /// Returns true if the specified keyword should be parsed as a table factor alias.
     /// When explicit is true, the keyword is preceded by an `AS` word. Parser is provided
     /// to enable looking ahead if needed.
-    fn is_table_factor_alias(&self, explicit: bool, kw: &Keyword, _parser: &mut Parser) -> bool {
-        explicit || !keywords::RESERVED_FOR_TABLE_ALIAS.contains(kw)
+    fn is_table_factor_alias(&self, explicit: bool, kw: &Keyword, parser: &mut Parser) -> bool {
+        explicit || self.is_table_alias(kw, parser)
     }
 
     /// Returns true if this dialect supports querying historical table data
diff --git a/src/dialect/snowflake.rs b/src/dialect/snowflake.rs
@@ -345,6 +345,85 @@ impl Dialect for SnowflakeDialect {
         }
     }
 
+    fn is_table_alias(&self, kw: &Keyword, parser: &mut Parser) -> bool {
+        match kw {
+            // The following keywords can be considered an alias as long as
+            // they are not followed by other tokens that may change their meaning
+            Keyword::LIMIT
+            | Keyword::RETURNING
+            | Keyword::INNER
+            | Keyword::USING
+            | Keyword::PIVOT
+            | Keyword::UNPIVOT
+            | Keyword::EXCEPT
+            | Keyword::MATCH_RECOGNIZE
+            | Keyword::OFFSET
+                if !matches!(parser.peek_token_ref().token, Token::SemiColon | Token::EOF) =>
+            {
+                false
+            }
+
+            // `FETCH` can be considered an alias as long as it's not followed by `FIRST`` or `NEXT`
+            // which would give it a different meanings, for example:
+            // `SELECT * FROM tbl FETCH FIRST 10 ROWS` - not an alias
+            // `SELECT * FROM tbl FETCH 10` - not an alias
+            Keyword::FETCH
+                if parser.peek_keyword(Keyword::FIRST)
+                    || parser.peek_keyword(Keyword::NEXT)
+                    || matches!(parser.peek_token().token, Token::Number(_, _)) =>
+            {
+                false
+            }
+
+            // All sorts of join-related keywords can be considered aliases unless additional
+            // keywords change their meaning.
+            Keyword::RIGHT | Keyword::LEFT | Keyword::SEMI | Keyword::ANTI
+                if parser
+                    .peek_one_of_keywords(&[Keyword::JOIN, Keyword::OUTER])
+                    .is_some() =>
+            {
+                false
+            }
+            Keyword::GLOBAL if parser.peek_keyword(Keyword::FULL) => false,
+
+            // Reserved keywords by the Snowflake dialect, which seem to be less strictive
+            // than what is listed in `keywords::RESERVED_FOR_TABLE_ALIAS`. The following
+            // keywords were tested with the this statement: `SELECT <KW>.* FROM tbl <KW>`.
+            Keyword::WITH
+            | Keyword::ORDER
+            | Keyword::SELECT
+            | Keyword::WHERE
+            | Keyword::GROUP
+            | Keyword::HAVING
+            | Keyword::LATERAL
+            | Keyword::UNION
+            | Keyword::INTERSECT
+            | Keyword::MINUS
+            | Keyword::ON
+            | Keyword::JOIN
+            | Keyword::INNER
+            | Keyword::CROSS
+            | Keyword::FULL
+            | Keyword::LEFT
+            | Keyword::RIGHT
+            | Keyword::NATURAL
+            | Keyword::USING
+            | Keyword::ASOF
+            | Keyword::MATCH_CONDITION
+            | Keyword::SET
+            | Keyword::QUALIFY
+            | Keyword::FOR
+            | Keyword::START
+            | Keyword::CONNECT
+            | Keyword::SAMPLE
+            | Keyword::TABLESAMPLE
+            | Keyword::FROM => false,
+
+            // Any other word is considered an alias
+            _ => true,
+        }
+    }
+
     /// See: <https://docs.snowflake.com/en/sql-reference/constructs/at-before>
     fn supports_timestamp_versioning(&self) -> bool {
         true
diff --git a/tests/sqlparser_common.rs b/tests/sqlparser_common.rs
@@ -5544,7 +5544,8 @@ fn parse_named_window_functions() {
                WINDOW w AS (PARTITION BY x), win AS (ORDER BY y)";
     supported_dialects.verified_stmt(sql);
 
-    let select = verified_only_select(sql);
+    let select = all_dialects_except(|d| d.is_table_alias(&Keyword::WINDOW, &mut Parser::new(d)))
+        .verified_only_select(sql);
 
     const EXPECTED_PROJ_QTY: usize = 2;
     assert_eq!(EXPECTED_PROJ_QTY, select.projection.len());
@@ -5574,6 +5575,7 @@ fn parse_named_window_functions() {
 
 #[test]
 fn parse_window_clause() {
+    let dialects = all_dialects_except(|d| d.is_table_alias(&Keyword::WINDOW, &mut Parser::new(d)));
     let sql = "SELECT * \
     FROM mytable \
     WINDOW \
@@ -5586,10 +5588,14 @@ fn parse_window_clause() {
         window7 AS (window1 ROWS UNBOUNDED PRECEDING), \
         window8 AS (window1 PARTITION BY a ORDER BY b ROWS UNBOUNDED PRECEDING) \
     ORDER BY C3";
-    verified_only_select(sql);
+    dialects.verified_only_select(sql);
 
     let sql = "SELECT * from mytable WINDOW window1 AS window2";
-    let dialects = all_dialects_except(|d| d.is::<BigQueryDialect>() || d.is::<GenericDialect>());
+    let dialects = all_dialects_except(|d| {
+        d.is::<BigQueryDialect>()
+            || d.is::<GenericDialect>()
+            || d.is_table_alias(&Keyword::WINDOW, &mut Parser::new(d))
+    });
     let res = dialects.parse_sql_statements(sql);
     assert_eq!(
         ParserError::ParserError("Expected: (, found: window2".to_string()),
@@ -5599,14 +5605,15 @@ fn parse_window_clause() {
 
 #[test]
 fn test_parse_named_window() {
+    let dialects = all_dialects_except(|d| d.is_table_alias(&Keyword::WINDOW, &mut Parser::new(d)));
     let sql = "SELECT \
     MIN(c12) OVER window1 AS min1, \
     MAX(c12) OVER window2 AS max1 \
     FROM aggregate_test_100 \
     WINDOW window1 AS (ORDER BY C12), \
     window2 AS (PARTITION BY C11) \
     ORDER BY C3";
-    let actual_select_only = verified_only_select(sql);
+    let actual_select_only = dialects.verified_only_select(sql);
     let expected = Select {
         select_token: AttachedToken::empty(),
         distinct: None,
@@ -5755,14 +5762,18 @@ fn test_parse_named_window() {
 
 #[test]
 fn parse_window_and_qualify_clause() {
+    let dialects = all_dialects_except(|d| {
+        d.is_table_alias(&Keyword::WINDOW, &mut Parser::new(d))
+            || d.is_table_alias(&Keyword::QUALIFY, &mut Parser::new(d))
+    });
     let sql = "SELECT \
     MIN(c12) OVER window1 AS min1 \
     FROM aggregate_test_100 \
     QUALIFY ROW_NUMBER() OVER my_window \
     WINDOW window1 AS (ORDER BY C12), \
     window2 AS (PARTITION BY C11) \
     ORDER BY C3";
-    verified_only_select(sql);
+    dialects.verified_only_select(sql);
 
     let sql = "SELECT \
     MIN(c12) OVER window1 AS min1 \
@@ -5771,7 +5782,7 @@ fn parse_window_and_qualify_clause() {
     window2 AS (PARTITION BY C11) \
     QUALIFY ROW_NUMBER() OVER my_window \
     ORDER BY C3";
-    verified_only_select(sql);
+    dialects.verified_only_select(sql);
 }
 
 #[test]
@@ -7439,7 +7450,8 @@ fn parse_join_syntax_variants() {
         "SELECT c1 FROM t1 FULL JOIN t2 USING(c1)",
     );
 
-    let res = parse_sql_statements("SELECT * FROM a OUTER JOIN b ON 1");
+    let dialects = all_dialects_except(|d| d.is_table_alias(&Keyword::OUTER, &mut Parser::new(d)));
+    let res = dialects.parse_sql_statements("SELECT * FROM a OUTER JOIN b ON 1");
     assert_eq!(
         ParserError::ParserError("Expected: APPLY, found: JOIN".to_string()),
         res.unwrap_err()
diff --git a/tests/sqlparser_snowflake.rs b/tests/sqlparser_snowflake.rs
@@ -3472,6 +3472,57 @@ fn test_sql_keywords_as_select_item_aliases() {
     }
 }
 
+#[test]
+fn test_sql_keywords_as_table_aliases() {
+    // Some keywords that should be parsed as an alias implicitly
+    let unreserved_kws = vec![
+        "VIEW",
+        "EXPLAIN",
+        "ANALYZE",
+        "SORT",
+        "PIVOT",
+        "UNPIVOT",
+        "TOP",
+        "LIMIT",
+        "OFFSET",
+        "FETCH",
+        "EXCEPT",
+        "CLUSTER",
+        "DISTRIBUTE",
+        "GLOBAL",
+        "ANTI",
+        "SEMI",
+        "RETURNING",
+        "OUTER",
+        "WINDOW",
+        "END",
+        "PARTITION",
+        "PREWHERE",
+        "SETTINGS",
+        "FORMAT",
+        "MATCH_RECOGNIZE",
+        "OPEN",
+    ];
+
+    for kw in unreserved_kws {
+        snowflake().verified_stmt(&format!("SELECT * FROM tbl AS {kw}"));
+        snowflake().one_statement_parses_to(
+            &format!("SELECT * FROM tbl {kw}"),
+            &format!("SELECT * FROM tbl AS {kw}"),
+        );
+    }
+
+    // Some keywords that should not be parsed as an alias implicitly
+    let reserved_kws = vec![
+        "FROM", "GROUP", "HAVING", "ORDER", "SELECT", "UNION", "WHERE", "WITH",
+    ];
+    for kw in reserved_kws {
+        assert!(snowflake()
+            .parse_sql_statements(&format!("SELECT * FROM tbl {kw}"))
+            .is_err());
+    }
+}
+
 #[test]
 fn test_timetravel_at_before() {
     snowflake().verified_only_select("SELECT * FROM tbl AT(TIMESTAMP => '2024-12-15 00:00:00')");
@@ -4232,3 +4283,8 @@ fn test_snowflake_create_view_with_composite_policy_name() {
         r#"CREATE VIEW X (COL WITH MASKING POLICY foo.bar.baz) AS SELECT * FROM Y"#;
     snowflake().verified_stmt(create_view_with_tag);
 }
+
+#[test]
+fn test_x() {
+    snowflake().parse_sql_statements("SELECT foo FROM (SELECT * FROM bar OFFSET 2 ROWS FETCH FIRST 2 ROWS ONLY) OFFSET 2 ROWS FETCH FIRST 2 ROWS ONLY").unwrap();
+}
