From f5764910c48ea51d160c6a1eca3f6f91bd323de0 Mon Sep 17 00:00:00 2001
From: Amos Bird <amosbird@gmail.com>
Date: Tue, 10 Jul 2018 22:24:19 +0800
Subject: [PATCH] Fix TRUNCATE command for temporary tables.

---
 .../src/Interpreters/InterpreterDropQuery.cpp | 29 +++++++++++++------
 .../00670_truncate_temporary_table.reference  |  5 ++++
 .../00670_truncate_temporary_table.sql        | 16 ++++++++++
 3 files changed, 41 insertions(+), 9 deletions(-)
 create mode 100644 dbms/tests/queries/0_stateless/00670_truncate_temporary_table.reference
 create mode 100644 dbms/tests/queries/0_stateless/00670_truncate_temporary_table.sql

diff --git a/dbms/src/Interpreters/InterpreterDropQuery.cpp b/dbms/src/Interpreters/InterpreterDropQuery.cpp
index cdb107a13ad..efe6aae87a8 100644
--- a/dbms/src/Interpreters/InterpreterDropQuery.cpp
+++ b/dbms/src/Interpreters/InterpreterDropQuery.cpp
@@ -121,18 +121,29 @@ BlockIO InterpreterDropQuery::executeToTemporaryTable(String & table_name, ASTDr
 {
     if (kind == ASTDropQuery::Kind::Detach)
         throw Exception("Unable to detach temporary table.", ErrorCodes::SYNTAX_ERROR);
-    else if (kind == ASTDropQuery::Kind::Drop)
+    else
     {
-        StoragePtr table = (context.hasSessionContext() ? context.getSessionContext() : context).tryRemoveExternalTable(table_name);
+        auto & context_handle = context.hasSessionContext() ? context.getSessionContext() : context;
+        StoragePtr table = context_handle.tryGetExternalTable(table_name);
         if (table)
         {
-            table->shutdown();
-            /// If table was already dropped by anyone, an exception will be thrown
-            auto table_lock = table->lockForAlter(__PRETTY_FUNCTION__);
-            /// Delete table data
-            table->drop();
-            table->is_dropped = true;
-            return {};
+            if (kind == ASTDropQuery::Kind::Truncate)
+            {
+                /// If table was already dropped by anyone, an exception will be thrown
+                auto table_lock = table->lockDataForAlter(__PRETTY_FUNCTION__);
+                /// Drop table data, don't touch metadata
+                table->truncate(query_ptr);
+            }
+            else if (kind == ASTDropQuery::Kind::Drop)
+            {
+                context_handle.tryRemoveExternalTable(table_name);
+                table->shutdown();
+                /// If table was already dropped by anyone, an exception will be thrown
+                auto table_lock = table->lockForAlter(__PRETTY_FUNCTION__);
+                /// Delete table data
+                table->drop();
+                table->is_dropped = true;
+            }
         }
     }
 
diff --git a/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.reference b/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.reference
new file mode 100644
index 00000000000..ddfc922fc29
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.reference
@@ -0,0 +1,5 @@
+======Before Truncate======
+0
+======After Truncate And Empty======
+======After Truncate And Insert Data======
+0
diff --git a/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.sql b/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.sql
new file mode 100644
index 00000000000..60e7f216f99
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00670_truncate_temporary_table.sql
@@ -0,0 +1,16 @@
+drop table if exists test;
+create temporary table test(id int);
+
+select '======Before Truncate======';
+insert into test values(0);
+select * from test;
+
+select '======After Truncate And Empty======';
+truncate table test;
+select * from test;
+
+select '======After Truncate And Insert Data======';
+insert into test values(0);
+select * from test;
+
+drop table if exists test;