fix(mysql)!: full MODIFY COLUMN support.

sqlglot/expressions/ddl.py

@@ -245,6 +245,10 @@ class AlterColumn(Expression):
     }
 
 
+class ModifyColumn(Expression):
+    pass
+
+
 class AlterIndex(Expression):
     arg_types = {"this": True, "visible": True}
 

sqlglot/generators/mysql.py

@@ -718,6 +718,9 @@ def altercolumn_sql(self, expression: exp.AlterColumn) -> str:
         this = self.sql(expression, "this")
         return f"MODIFY COLUMN {this} {dtype}"
 
+    def modifycolumn_sql(self, expression: exp.ModifyColumn) -> str:
+        return f"MODIFY COLUMN {self.sql(expression, 'this')}"
+
     def _prefixed_sql(self, prefix: str, expression: exp.Expr, arg: str) -> str:
         sql = self.sql(expression, arg)
         return f" {prefix} {sql}" if sql else ""

sqlglot/parsers/mysql.py

@@ -252,7 +252,7 @@ class MySQLParser(parser.Parser):
 
     ALTER_PARSERS = {
         **parser.Parser.ALTER_PARSERS,
-        "MODIFY": lambda self: self._parse_alter_table_alter(),
+        "MODIFY": lambda self: self._parse_alter_table_modify(),
         "AUTO_INCREMENT": lambda self: self._parse_property_assignment(exp.AutoIncrementProperty),
     }
 
@@ -315,6 +315,27 @@ def _parse_alter_drop_action(self) -> exp.Expr | None:
             return self.expression(exp.DropPrimaryKey())
         return super()._parse_alter_drop_action()
 
+    def _parse_alter_table_modify(self) -> exp.Expr | None:
+        self._match(TokenType.COLUMN)
+
+        column = self._parse_field(any_token=True)
+        if column is None:
+            return None
+
+        column_def = self._parse_column_def(column)
+        if not isinstance(column_def, exp.ColumnDef):
+            return None
+
+        if self._match_texts(("FIRST", "AFTER")):
+            keyword = self._prev.text.upper()
+            target = self._parse_column() if keyword == "AFTER" else None
+            column_def.set(
+                "position",
+                self.expression(exp.ColumnPosition(this=target, position=keyword)),
+            )
+
+        return self.expression(exp.ModifyColumn(this=column_def))
+
     def _parse_generated_as_identity(
         self,
     ) -> (

tests/dialects/test_mysql.py

@@ -38,6 +38,18 @@ def test_ddl(self):
         self.validate_identity("ALTER TABLE t DROP PRIMARY KEY")
         self.validate_identity("ALTER TABLE t DROP COLUMN c, DROP PRIMARY KEY, DROP INDEX `i`")
         self.validate_identity("ALTER TABLE test_table MODIFY COLUMN test_column LONGTEXT")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT NOT NULL")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT DEFAULT 5")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT NOT NULL DEFAULT 5")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c VARCHAR(50) NOT NULL DEFAULT 'foo'")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT COMMENT 'hi'")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT FIRST")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT AFTER d")
+        self.validate_identity("ALTER TABLE t MODIFY COLUMN c INT NOT NULL AFTER d")
+        self.validate_identity(
+            "ALTER TABLE t MODIFY c INT NOT NULL",
+            "ALTER TABLE t MODIFY COLUMN c INT NOT NULL",
+        )
         self.validate_identity("ALTER TABLE t AUTO_INCREMENT=3000000000")
         self.validate_identity("ALTER VIEW v AS SELECT a, b, c, d FROM foo")
         self.validate_identity("ALTER VIEW v AS SELECT * FROM foo WHERE c > 100")