Add support for ALTER TABLE DROP INDEX

src/ast/ddl.rs

@@ -187,6 +187,12 @@ pub enum AlterTableOperation {
     DropForeignKey {
         name: Ident,
     },
+    /// `DROP INDEX <index_name>`
+    ///
+    /// [MySQL]: https://dev.mysql.com/doc/refman/8.4/en/alter-table.html
+    DropIndex {
+        name: Ident,
+    },
     /// `ENABLE ALWAYS RULE rewrite_rule_name`
     ///
     /// Note: this is a PostgreSQL-specific operation.
@@ -606,6 +612,7 @@ impl fmt::Display for AlterTableOperation {
             }
             AlterTableOperation::DropPrimaryKey => write!(f, "DROP PRIMARY KEY"),
             AlterTableOperation::DropForeignKey { name } => write!(f, "DROP FOREIGN KEY {name}"),
+            AlterTableOperation::DropIndex { name } => write!(f, "DROP INDEX {name}"),
             AlterTableOperation::DropColumn {
                 has_column_keyword,
                 column_name,

src/ast/spans.rs

@@ -1111,6 +1111,7 @@ impl Spanned for AlterTableOperation {
                 .union_opt(&with_name.as_ref().map(|n| n.span)),
             AlterTableOperation::DropPrimaryKey => Span::empty(),
             AlterTableOperation::DropForeignKey { name } => name.span,
+            AlterTableOperation::DropIndex { name } => name.span,
             AlterTableOperation::EnableAlwaysRule { name } => name.span,
             AlterTableOperation::EnableAlwaysTrigger { name } => name.span,
             AlterTableOperation::EnableReplicaRule { name } => name.span,

src/parser/mod.rs

@@ -8611,6 +8611,9 @@ impl<'a> Parser<'a> {
             } else if self.parse_keywords(&[Keyword::FOREIGN, Keyword::KEY]) {
                 let name = self.parse_identifier()?;
                 AlterTableOperation::DropForeignKey { name }
+            } else if self.parse_keyword(Keyword::INDEX) {
+                let name = self.parse_identifier()?;
+                AlterTableOperation::DropIndex { name }
             } else if self.parse_keyword(Keyword::PROJECTION)
                 && dialect_of!(self is ClickHouseDialect|GenericDialect)
             {

tests/sqlparser_mysql.rs

@@ -4018,3 +4018,13 @@ fn parse_drop_index() {
         _ => unreachable!(),
     }
 }
+
+#[test]
+fn parse_alter_table_drop_index() {
+    assert_matches!(
+        alter_table_op(
+            mysql_and_generic().verified_stmt("ALTER TABLE tab DROP INDEX idx_index")
+        ),
+        AlterTableOperation::DropIndex { name } if name.value == "idx_index"
+    );
+}