planner: skip index scan plan for tablesample (#54016)

close #54015

pkg/planner/core/find_best_task.go

@@ -1521,6 +1521,10 @@ func (ds *DataSource) FindBestTask(prop *property.PhysicalProperty, planCounter
 		if ds.preferStoreType&h.PreferTiFlash != 0 {
 			continue
 		}
+		// TableSample do not support index scan.
+		if ds.SampleInfo != nil {
+			continue
+		}
 		idxTask, err := ds.convertToIndexScan(prop, candidate, opt)
 		if err != nil {
 			return nil, 0, err

tests/integrationtest/r/executor/sample.result

@@ -194,7 +194,7 @@ a
 2100
 4500
 select a from t use index (idx_0) tablesample regions() order by a;
-Error 8128 (HY000): Invalid TABLESAMPLE: plan not supported
+Error 1815 (HY000): Internal : Can't find a proper physical plan for this query
 DROP TABLE IF EXISTS a;
 CREATE TABLE a (pk bigint unsigned primary key clustered, v text);
 INSERT INTO a WITH RECURSIVE b(pk) AS (SELECT 1 UNION ALL SELECT pk+1 FROM b WHERE pk < 1000) SELECT pk, 'a' FROM b;
@@ -224,3 +224,7 @@ a	b
 1	1
 2	2
 set @@tidb_partition_prune_mode=default;
+drop table if exists t;
+create table t (a decimal(62,2) not null, key idx (a), primary key (a) clustered);
+select a from t tablesample regions() order by a;
+a

tests/integrationtest/t/executor/sample.test

@@ -119,7 +119,7 @@ split table t between (0) and (10000) regions 5;
 insert into t values (1000, 1, '1'), (1001, 1, '1'), (2100, 2, '2'), (4500, 3, '3');
 create index idx_0 on t (b);
 select a from t tablesample regions() order by a;
--- error 8128
+-- error 1815
 select a from t use index (idx_0) tablesample regions() order by a;
 
 # TestTableSampleUnsignedIntHandle
@@ -143,3 +143,8 @@ select * from t tablesample regions() order by a;
 set @@tidb_partition_prune_mode='dynamic';
 select * from t tablesample regions() order by a;
 set @@tidb_partition_prune_mode=default;
+
+# TestTableSampleNoIndexScan
+drop table if exists t;
+create table t (a decimal(62,2) not null, key idx (a), primary key (a) clustered);
+select a from t tablesample regions() order by a;