Fix a crash on zero-shard tables

src/backend/distributed/planner/shard_pruning.c

@@ -216,12 +216,19 @@ List *
 PruneShards(Oid relationId, Index rangeTableId, List *whereClauseList)
 {
 	DistTableCacheEntry *cacheEntry = DistributedTableCacheEntry(relationId);
+	int shardCount = cacheEntry->shardIntervalArrayLength;
 	char partitionMethod = cacheEntry->partitionMethod;
 	ClauseWalkerContext context = { 0 };
 	ListCell *pruneCell;
 	List *prunedList = NIL;
 	bool foundRestriction = false;
 
+	/* there are no shards to return */
+	if (shardCount == 0)
+	{
+		return NIL;
+	}
+
 	/* always return empty result if WHERE clause is of the form: false (AND ..) */
 	if (ContainsFalseClause(whereClauseList))
 	{

src/test/regress/expected/multi_create_table.out

@@ -387,6 +387,46 @@ SELECT * FROM data_load_test ORDER BY col1;
 (2 rows)
 
 DROP TABLE data_load_test;
+-- test queries on distributed tables with no shards
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT create_distributed_table('no_shard_test', 'col1', 'append');
+ create_distributed_table 
+--------------------------
+ 
+(1 row)
+
+SELECT * FROM no_shard_test WHERE col1 > 1;
+ col1 | col2 
+------+------
+(0 rows)
+
+DROP TABLE no_shard_test;
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT create_distributed_table('no_shard_test', 'col1', 'range');
+ create_distributed_table 
+--------------------------
+ 
+(1 row)
+
+SELECT * FROM no_shard_test WHERE col1 > 1;
+ col1 | col2 
+------+------
+(0 rows)
+
+DROP TABLE no_shard_test;
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT master_create_distributed_table('no_shard_test', 'col1', 'hash');
+ master_create_distributed_table 
+---------------------------------
+ 
+(1 row)
+
+SELECT * FROM no_shard_test WHERE col1 > 1;
+ col1 | col2 
+------+------
+(0 rows)
+
+DROP TABLE no_shard_test;
 -- ensure writes in the same transaction as create_distributed_table are visible
 BEGIN;
 CREATE TABLE data_load_test (col1 int, col2 text, col3 serial);

src/test/regress/sql/multi_create_table.sql

@@ -206,6 +206,22 @@ SELECT create_distributed_table('data_load_test', 'col1');
 SELECT * FROM data_load_test ORDER BY col1;
 DROP TABLE data_load_test;
 
+-- test queries on distributed tables with no shards
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT create_distributed_table('no_shard_test', 'col1', 'append');
+SELECT * FROM no_shard_test WHERE col1 > 1;
+DROP TABLE no_shard_test;
+
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT create_distributed_table('no_shard_test', 'col1', 'range');
+SELECT * FROM no_shard_test WHERE col1 > 1;
+DROP TABLE no_shard_test;
+
+CREATE TABLE no_shard_test (col1 int, col2 text);
+SELECT master_create_distributed_table('no_shard_test', 'col1', 'hash');
+SELECT * FROM no_shard_test WHERE col1 > 1;
+DROP TABLE no_shard_test;
+
 -- ensure writes in the same transaction as create_distributed_table are visible
 BEGIN;
 CREATE TABLE data_load_test (col1 int, col2 text, col3 serial);