fix(mysql): parse quoted constraint names. (#7519)

sqlglot's `_parse_unique_key` checks whether the current token matches a
`CONSTRAINT_PARSERS` keyword to decide if it should stop parsing the
index name. The check used `self._curr.text.upper()` without considering
the token type, so backtick-quoted identifiers like `` `Unique` ``, ``
`Index` ``, and `` `Key` `` were mistaken for constraint keywords and
rejected.

MySQL allows any identifier as an index name when it is quoted.  The
tokenizer already classifies these as `TokenType.IDENTIFIER`, so the fix
adds a `token_type != TokenType.IDENTIFIER` guard to the existing check.
Quoted names skip the keyword lookup entirely and fall through to
`_parse_id_var` as intended.

Author: burnison

sqlglot/parser.py

@@ -7262,7 +7262,11 @@ def _parse_unnamed_constraint(
         return result
 
     def _parse_unique_key(self) -> exp.Expr | None:
-        if self._curr and self._curr.text.upper() in self.CONSTRAINT_PARSERS:
+        if (
+            self._curr
+            and self._curr.token_type != TokenType.IDENTIFIER
+            and self._curr.text.upper() in self.CONSTRAINT_PARSERS
+        ):
             return None
         return self._parse_id_var(any_token=False)
 

tests/dialects/test_mysql.py

@@ -144,6 +144,18 @@ def test_ddl(self):
             "CREATE TABLE IF NOT EXISTS industry_info (a BIGINT(20) NOT NULL AUTO_INCREMENT, b BIGINT(20) NOT NULL, c VARCHAR(1000), PRIMARY KEY (a), UNIQUE KEY d (b), KEY e (b))",
             "CREATE TABLE IF NOT EXISTS industry_info (a BIGINT(20) NOT NULL AUTO_INCREMENT, b BIGINT(20) NOT NULL, c VARCHAR(1000), PRIMARY KEY (a), UNIQUE d (b), INDEX e (b))",
         )
+        self.validate_identity(
+            "CREATE TABLE t (a INT, b INT, UNIQUE KEY `Unique` (a, b))",
+            "CREATE TABLE t (a INT, b INT, UNIQUE `Unique` (a, b))",
+        )
+        self.validate_identity(
+            "CREATE TABLE t (a INT, UNIQUE KEY `Index` (a))",
+            "CREATE TABLE t (a INT, UNIQUE `Index` (a))",
+        )
+        self.validate_identity(
+            "CREATE TABLE t (a INT, UNIQUE KEY `Key` (a))",
+            "CREATE TABLE t (a INT, UNIQUE `Key` (a))",
+        )
         self.validate_identity(
             "CREATE TABLE test (ts TIMESTAMP, ts_tz TIMESTAMPTZ, ts_ltz TIMESTAMPLTZ)",
             "CREATE TABLE test (ts TIMESTAMP, ts_tz TIMESTAMP, ts_ltz TIMESTAMP)",