Merge pull request #55822 from ajwerner/backport20.2-55766

release-20.2: sql: fix bug dropping shard column which is not the last column

pkg/sql/drop_index.go

@@ -158,14 +158,10 @@ func (n *dropIndexNode) dropShardColumnAndConstraint(
 	tableDesc.AddColumnMutation(shardColDesc, descpb.DescriptorMutation_DROP)
 	for i := range tableDesc.Columns {
 		if tableDesc.Columns[i].ID == shardColDesc.ID {
-			tmp := tableDesc.Columns[:0]
-			for j, col := range tableDesc.Columns {
-				if i == j {
-					continue
-				}
-				tmp = append(tmp, col)
-			}
-			tableDesc.Columns = tmp
+			// Note the third slice parameter which will force a copy of the backing
+			// array if the column being removed is not the last column.
+			tableDesc.Columns = append(tableDesc.Columns[:i:i],
+				tableDesc.Columns[i+1:]...)
 			break
 		}
 	}

pkg/sql/logictest/testdata/logic_test/hash_sharded_index

@@ -566,3 +566,24 @@ ALTER TABLE rename_column RENAME crdb_internal_c2_shard_8 TO foo;
 
 statement ok
 DROP TABLE rename_column;
+
+# This is a regression test for a bug whereby the dropping of a hash column
+# could result in an invalid descriptor and would fail. The underlying bug was
+# due to a column descriptor pointer to a slice being clobbered. See #55766.
+subtest drop_earlier_column_due_to_hash_sharded_index
+
+statement ok
+CREATE TABLE IF NOT EXISTS drop_earlier_hash_column (
+    i INT PRIMARY KEY,
+    j INT,
+    k INT
+);
+
+statement ok
+CREATE INDEX h1 ON drop_earlier_hash_column(j) USING HASH WITH BUCKET_COUNT = 8;
+
+statement ok
+CREATE INDEX h2 ON drop_earlier_hash_column(k) USING HASH WITH BUCKET_COUNT = 8;
+
+statement ok
+DROP INDEX h1;

pkg/sql/pgwire/testdata/pgtest/notice

@@ -55,7 +55,7 @@ Query {"String": "DROP INDEX t_x_idx"}
 until crdb_only
 CommandComplete
 ----
-{"Severity":"NOTICE","Code":"00000","Message":"the data for dropped indexes is reclaimed asynchronously","Detail":"","Hint":"The reclamation delay can be customized in the zone configuration for the table.","Position":0,"InternalPosition":0,"InternalQuery":"","Where":"","SchemaName":"","TableName":"","ColumnName":"","DataTypeName":"","ConstraintName":"","File":"drop_index.go","Line":524,"Routine":"dropIndexByName","UnknownFields":null}
+{"Severity":"NOTICE","Code":"00000","Message":"the data for dropped indexes is reclaimed asynchronously","Detail":"","Hint":"The reclamation delay can be customized in the zone configuration for the table.","Position":0,"InternalPosition":0,"InternalQuery":"","Where":"","SchemaName":"","TableName":"","ColumnName":"","DataTypeName":"","ConstraintName":"","File":"drop_index.go","Line":520,"Routine":"dropIndexByName","UnknownFields":null}
 {"Type":"CommandComplete","CommandTag":"DROP INDEX"}
 
 until noncrdb_only