Feat(mysql): add support for ALTER INDEX (#4800)

* Support MySQL's `ALTER INDEX`.

MySQL 8.0 and above [support] altering an existinq index, `x`, using the
syntax, `ALTER TABLE x ALTER INDEX {VISIBLE | INVISIBLE}`. This allows
for the index to become either invisible _or_ visible. No other index
changes are permitted.

This commit adds support for such syntax.

[support]: https://dev.mysql.com/doc/refman/8.0/en/alter-table.html

* Move `None` initialization to `else` branch

* Fix return type hint

* Apply styling change

---------

Co-authored-by: Jo <[email protected]>

Author: burnison

sqlglot/dialects/mysql.py

@@ -439,6 +439,11 @@ class Parser(parser.Parser):
             "MODIFY": lambda self: self._parse_alter_table_alter(),
         }
 
+        ALTER_ALTER_PARSERS = {
+            **parser.Parser.ALTER_ALTER_PARSERS,
+            "INDEX": lambda self: self._parse_alter_table_alter_index(),
+        }
+
         SCHEMA_UNNAMED_CONSTRAINTS = {
             *parser.Parser.SCHEMA_UNNAMED_CONSTRAINTS,
             "FULLTEXT",
@@ -693,6 +698,18 @@ def _parse_json_value(self) -> exp.JSONValue:
                 on_condition=self._parse_on_condition(),
             )
 
+        def _parse_alter_table_alter_index(self) -> exp.AlterIndex:
+            index = self._parse_field(any_token=True)
+
+            if self._match_text_seq("VISIBLE"):
+                visible = True
+            elif self._match_text_seq("INVISIBLE"):
+                visible = False
+            else:
+                visible = None
+
+            return self.expression(exp.AlterIndex, this=index, visible=visible)
+
     class Generator(generator.Generator):
         INTERVAL_ALLOWS_PLURAL_FORM = False
         LOCKING_READS_SUPPORTED = True

sqlglot/expressions.py

@@ -1706,6 +1706,11 @@ class AlterColumn(Expression):
     }
 
 
+# https://dev.mysql.com/doc/refman/8.0/en/invisible-indexes.html
+class AlterIndex(Expression):
+    arg_types = {"this": True, "visible": True}
+
+
 # https://docs.aws.amazon.com/redshift/latest/dg/r_ALTER_TABLE.html
 class AlterDistStyle(Expression):
     pass

sqlglot/generator.py

@@ -3304,6 +3304,14 @@ def altercolumn_sql(self, expression: exp.AlterColumn) -> str:
 
         return f"ALTER COLUMN {this} DROP DEFAULT"
 
+    def alterindex_sql(self, expression: exp.AlterIndex) -> str:
+        this = self.sql(expression, "this")
+
+        visible = expression.args.get("visible")
+        visible_sql = "VISIBLE" if visible else "INVISIBLE"
+
+        return f"ALTER INDEX {this} {visible_sql}"
+
     def alterdiststyle_sql(self, expression: exp.AlterDistStyle) -> str:
         this = self.sql(expression, "this")
         if not isinstance(expression.this, exp.Var):

tests/dialects/test_mysql.py

@@ -150,6 +150,8 @@ def test_ddl(self):
                 "sqlite": "CREATE TABLE x (id INTEGER NOT NULL AUTOINCREMENT PRIMARY KEY)",
             },
         )
+        self.validate_identity("ALTER TABLE t ALTER INDEX i INVISIBLE")
+        self.validate_identity("ALTER TABLE t ALTER INDEX i VISIBLE")
 
     def test_identity(self):
         self.validate_identity("SELECT HIGH_PRIORITY STRAIGHT_JOIN SQL_CALC_FOUND_ROWS * FROM t")