MsSql: Disallow unquoted FROM keyword as alias assignment expression (#2546)

Author: LucaCappelletti94

src/parser/mod.rs

@@ -19289,6 +19289,13 @@ impl<'a> Parser<'a> {
             } if self.dialect.supports_eq_alias_assignment()
                 && matches!(left.as_ref(), Expr::Identifier(_)) =>
             {
+                if matches!(right.as_ref(), Expr::Identifier(v) if v.value.to_lowercase() == "from" && v.quote_style.is_none())
+                {
+                    return parser_err!(
+                        format!("Expected an expression, found: {right}"),
+                        self.peek_token_ref().span.start
+                    );
+                }
                 let Expr::Identifier(alias) = *left else {
                     return parser_err!(
                         "BUG: expected identifier expression as alias",

tests/sqlparser_common.rs

@@ -15270,6 +15270,24 @@ fn test_alias_equal_expr() {
     let expected = r#"SELECT (a * b) AS some_alias FROM some_table"#;
     let _ = dialects.one_statement_parses_to(sql, expected);
 
+    let sql = r#"SELECT some_alias = "from" FROM some_table"#;
+    let expected = r#"SELECT "from" AS some_alias FROM some_table"#;
+    let _ = dialects.one_statement_parses_to(sql, expected);
+
+    assert_eq!(
+        dialects
+            .parse_sql_statements("SELECT a = FROM")
+            .unwrap_err(),
+        ParserError::ParserError("Expected an expression, found: FROM".to_string())
+    );
+
+    assert_eq!(
+        dialects
+            .parse_sql_statements("SELECT a = FROM some_table")
+            .unwrap_err(),
+        ParserError::ParserError("Expected an expression, found: FROM".to_string())
+    );
+
     let dialects = all_dialects_where(|d| !d.supports_eq_alias_assignment());
     let sql = r#"SELECT x = (a * b) FROM some_table"#;
     let expected = r#"SELECT x = (a * b) FROM some_table"#;

tests/sqlparser_mssql.rs

@@ -2942,6 +2942,11 @@ fn parse_bracket_quoted_function_argument_name() {
     );
 }
 
+#[test]
+fn parse_bracket_quoted_eq_alias_assignment() {
+    ms().one_statement_parses_to("SELECT a = [from] FROM t", "SELECT [from] AS a FROM t");
+}
+
 #[test]
 fn parse_create_proc() {
     ms().one_statement_parses_to(