From 667591080fc211c7a926e5881743b53fe0bed3cf Mon Sep 17 00:00:00 2001
From: DarkWanderer <elquentaro@gmail.com>
Date: Sat, 16 Jan 2021 15:30:15 +0300
Subject: [PATCH] DataReader: do not throw exception on empty dataset #58

---
 ClickHouse.Client.Tests/SqlAlterTests.cs              | 4 ++--
 ClickHouse.Client/ADO/Readers/ClickHouseDataReader.cs | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/ClickHouse.Client.Tests/SqlAlterTests.cs b/ClickHouse.Client.Tests/SqlAlterTests.cs
index ed77235e..3bfe1b10 100644
--- a/ClickHouse.Client.Tests/SqlAlterTests.cs
+++ b/ClickHouse.Client.Tests/SqlAlterTests.cs
@@ -21,8 +21,8 @@ public SqlAlterTests()
         [Test]
         public async Task ShouldExecuteAlterTable()
         {
-            await connection.ExecuteStatementAsync($"CREATE TABLE IF NOT EXISTS test.table_delete_from (value Int32) ENGINE=MergeTree ORDER BY value");
-            await connection.ExecuteStatementAsync($"ALTER TABLE test.table_delete_from DELETE WHERE 1=1");
+            await connection.ExecuteScalarAsync($"CREATE TABLE IF NOT EXISTS test.table_delete_from (value Int32) ENGINE=MergeTree ORDER BY value");
+            await connection.ExecuteScalarAsync($"ALTER TABLE test.table_delete_from DELETE WHERE 1=1");
         }
     }
 }
diff --git a/ClickHouse.Client/ADO/Readers/ClickHouseDataReader.cs b/ClickHouse.Client/ADO/Readers/ClickHouseDataReader.cs
index e1ed709f..f5de2a66 100644
--- a/ClickHouse.Client/ADO/Readers/ClickHouseDataReader.cs
+++ b/ClickHouse.Client/ADO/Readers/ClickHouseDataReader.cs
@@ -161,6 +161,13 @@ protected override void Dispose(bool disposing)
 
         private void ReadHeaders()
         {
+            if (reader.PeekChar() == -1)
+            {
+                // Empty dataset
+                FieldNames = new string[0];
+                RawTypes = new ClickHouseType[0];
+                return;
+            }
             var count = reader.Read7BitEncodedInt();
             FieldNames = new string[count];
             RawTypes = new ClickHouseType[count];