From ef74a745f9f9c4dee21ac00658071a80dab4e64d Mon Sep 17 00:00:00 2001
From: Ti Chi Robot <ti-community-prow-bot@tidb.io>
Date: Tue, 18 Jan 2022 14:25:45 +0800
Subject: [PATCH] fix cast expr when arg is zero length string (#3882) (#3885)

---
 dbms/src/Functions/FunctionsString.cpp        | 24 +++++++++++++++
 .../fullstack-test/expr/cast_nullability.test | 30 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/dbms/src/Functions/FunctionsString.cpp b/dbms/src/Functions/FunctionsString.cpp
index 3a2200b5f8c..f1d32f75d4e 100644
--- a/dbms/src/Functions/FunctionsString.cpp
+++ b/dbms/src/Functions/FunctionsString.cpp
@@ -2839,6 +2839,12 @@ class tidbPadImpl
                     vec_result_null_map[i] = tidbPadOneRow<IsLeft>(&string_data[string_prev_offset], string_offsets[i] - string_prev_offset, static_cast<int32_t>(target_len), &(*padding_data)[padding_prev_offset], (*padding_offsets)[i] - padding_prev_offset, result_data, res_prev_offset);
                 }
             }
+            else
+            {
+                result_data.resize(result_data.size() + 1);
+                result_data[res_prev_offset] = '\0';
+                res_prev_offset++;
+            }
 
             string_prev_offset = string_offsets[i];
             padding_prev_offset = (*padding_offsets)[i];
@@ -2870,6 +2876,12 @@ class tidbPadImpl
                     vec_result_null_map[i] = tidbPadOneRow<IsLeft>(&string_data[string_prev_offset], string_offsets[i] - string_prev_offset, static_cast<int32_t>(target_len), padding, padding_size, result_data, res_prev_offset);
                 }
             }
+            else
+            {
+                result_data.resize(result_data.size() + 1);
+                result_data[res_prev_offset] = '\0';
+                res_prev_offset++;
+            }
 
             string_prev_offset = string_offsets[i];
             result_offsets[i] = res_prev_offset;
@@ -2900,6 +2912,12 @@ class tidbPadImpl
                     vec_result_null_map[i] = tidbPadOneRow<IsLeft>(reinterpret_cast<const UInt8 *>(str_val.c_str()), str_val.size() + 1, static_cast<int32_t>(target_len), &(*padding_data)[padding_prev_offset], (*padding_offsets)[i] - padding_prev_offset, result_data, res_prev_offset);
                 }
             }
+            else
+            {
+                result_data.resize(result_data.size() + 1);
+                result_data[res_prev_offset] = '\0';
+                res_prev_offset++;
+            }
 
             padding_prev_offset = (*padding_offsets)[i];
             result_offsets[i] = res_prev_offset;
@@ -2929,6 +2947,12 @@ class tidbPadImpl
                     vec_result_null_map[i] = tidbPadOneRow<IsLeft>(reinterpret_cast<const UInt8 *>(str_val.c_str()), str_val.size() + 1, static_cast<int32_t>(target_len), padding, padding_size, result_data, res_prev_offset);
                 }
             }
+            else
+            {
+                result_data.resize(result_data.size() + 1);
+                result_data[res_prev_offset] = '\0';
+                res_prev_offset++;
+            }
 
             result_offsets[i] = res_prev_offset;
         }
diff --git a/tests/fullstack-test/expr/cast_nullability.test b/tests/fullstack-test/expr/cast_nullability.test
index 622e1366d92..a53e62e1492 100644
--- a/tests/fullstack-test/expr/cast_nullability.test
+++ b/tests/fullstack-test/expr/cast_nullability.test
@@ -2,8 +2,13 @@ mysql> drop table if exists test.t
 mysql> create table test.t(a int not null )
 mysql> insert into test.t values(1),(2)
 mysql> alter table test.t set tiflash replica 1 
+mysql> drop table if exists test.t1;
+mysql> create table test.t1(c1 varchar(100));
+mysql> insert into test.t1 values(null);
+mysql> alter table test.t1 set tiflash replica 1;
 
 func> wait_table test t
+func> wait_table test t1
 
 mysql> use test; set @@tidb_isolation_read_engines='tiflash'; select * from test.t union all select * from test.t
 +---+
@@ -24,3 +29,28 @@ mysql> use test; set @@tidb_isolation_read_engines='tiflash'; select count(*) ,
 +----------+----+
 
 mysql> drop table if exists test.t
+
+mysql> set tidb_isolation_read_engines='tiflash'; set tidb_enforce_mpp=1; select cast(lpad(test.t1.c1, 1, 'b') as datetime) from test.t1;
++--------------------------------------------+
+| cast(lpad(test.t1.c1, 1, 'b') as datetime) |
++--------------------------------------------+
+| NULL                                       |
++--------------------------------------------+
+mysql> set tidb_isolation_read_engines='tiflash'; set tidb_enforce_mpp=1; select cast(lpad(test.t1.c1, 1, 'b') as decimal) from test.t1;
++-------------------------------------------+
+| cast(lpad(test.t1.c1, 1, 'b') as decimal) |
++-------------------------------------------+
+|                                      NULL |
++-------------------------------------------+
+mysql> set tidb_isolation_read_engines='tiflash'; set tidb_enforce_mpp=1; select cast(lpad(test.t1.c1, 1, 'b') as signed) from test.t1;
++------------------------------------------+
+| cast(lpad(test.t1.c1, 1, 'b') as signed) |
++------------------------------------------+
+|                                     NULL |
++------------------------------------------+
+mysql> set tidb_isolation_read_engines='tiflash'; set tidb_enforce_mpp=1; select cast(lpad(test.t1.c1, 1, 'b') as double) from test.t1;
++------------------------------------------+
+| cast(lpad(test.t1.c1, 1, 'b') as double) |
++------------------------------------------+
+|                                     NULL |
++------------------------------------------+