Bug #21103101 SORTING SKIPPED WHEN DROPPING THE

		SINGLE COLUMN PRIMARY KEY
Description:
	- Don't skip sorting during rebuilding of the table
when single column primary key is dropped.

Reviewed-by: Marko Mäkelä <[email protected]>
Approved via IM.

Author: Thirunarayanan

mysql-test/suite/innodb/r/innodb-index.result

@@ -1582,3 +1582,18 @@ a	b
 0	khdHps6UxW8Lwaoxa604oK6zkb
 1	khdHps6UtW8L
 drop table t1;
+#
+# Bug #21103101	SORTING SKIPPED WHEN DROPPING THE SINGLE
+#			COLUMN PRIMARY KEY
+#
+create table t1(f1 int not null, f2 int not null,
+primary key (f1), unique key(f1, f2))engine=innodb;
+insert into t1 values(1,3), (2,2);
+alter table t1 drop column f1;
+drop table t1;
+create table t1(f1 int not null, f2 int not null,
+primary key (f1), unique key(f1, f2))engine=innodb;
+insert into t1 values(1,3), (2,2);
+alter table t1 drop primary key, lock=none;
+ERROR 0A000: LOCK=NONE is not supported. Reason: Dropping a primary key is not allowed without also adding a new primary key. Try LOCK=SHARED.
+drop table t1;

mysql-test/suite/innodb/t/innodb-index.test

@@ -852,3 +852,23 @@ alter table t1 drop primary key, add primary key (b(8),a);
 select * from t1;
 drop table t1;
 
+
+--echo #
+--echo # Bug #21103101	SORTING SKIPPED WHEN DROPPING THE SINGLE
+--echo #			COLUMN PRIMARY KEY
+--echo #
+
+# Drop primary key column.
+create table t1(f1 int not null, f2 int not null,
+		primary key (f1), unique key(f1, f2))engine=innodb;
+insert into t1 values(1,3), (2,2);
+alter table t1 drop column f1;
+drop table t1;
+
+# Drop Primary key when lock is none.
+create table t1(f1 int not null, f2 int not null,
+		primary key (f1), unique key(f1, f2))engine=innodb;
+insert into t1 values(1,3), (2,2);
+--error ER_ALTER_OPERATION_NOT_SUPPORTED_REASON
+alter table t1 drop primary key, lock=none;
+drop table t1;

storage/innobase/handler/handler0alter.cc

@@ -2749,6 +2749,13 @@ innobase_pk_order_preserved(
 			old_field++;
 			new_field++;
 		} else if (old_col_no == ULINT_UNDEFINED) {
+
+			if (old_n_fields == 1) {
+				/* Dropping single column primary key
+				requires sorting. */
+				return(false);
+			}
+
 			pk_col_dropped = true;
 			old_field++;
 		} else {