From c37b55c3b176df834144208a556f971762734a21 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Thu, 17 Sep 2020 00:19:58 +0300
Subject: [PATCH] Fix error in "extractAllGroups" function

---
 src/Functions/extractAllGroups.h                            | 6 ++++--
 .../01497_extract_all_groups_empty_match.reference          | 2 ++
 .../0_stateless/01497_extract_all_groups_empty_match.sql    | 2 ++
 3 files changed, 8 insertions(+), 2 deletions(-)
 create mode 100644 tests/queries/0_stateless/01497_extract_all_groups_empty_match.reference
 create mode 100644 tests/queries/0_stateless/01497_extract_all_groups_empty_match.sql

diff --git a/src/Functions/extractAllGroups.h b/src/Functions/extractAllGroups.h
index d6ec9fadb73..f1168c2ebc2 100644
--- a/src/Functions/extractAllGroups.h
+++ b/src/Functions/extractAllGroups.h
@@ -129,7 +129,9 @@ public:
                     for (size_t group = 1; group <= groups_count; ++group)
                         data_col->insertData(matched_groups[group].data(), matched_groups[group].size());
 
-                    pos = matched_groups[0].data() + matched_groups[0].size();
+                    /// If match is empty - it's technically Ok but we have to shift one character nevertheless
+                    /// to avoid infinite loop.
+                    pos = matched_groups[0].data() + std::max<size_t>(1, matched_groups[0].size());
 
                     current_nested_offset += groups_count;
                     nested_offsets_data.push_back(current_nested_offset);
@@ -167,7 +169,7 @@ public:
                     for (size_t group = 1; group <= groups_count; ++group)
                         all_matches.push_back(matched_groups[group]);
 
-                    pos = matched_groups[0].data() + matched_groups[0].size();
+                    pos = matched_groups[0].data() + std::max<size_t>(1, matched_groups[0].size());
 
                     ++matches_per_row;
                 }
diff --git a/tests/queries/0_stateless/01497_extract_all_groups_empty_match.reference b/tests/queries/0_stateless/01497_extract_all_groups_empty_match.reference
new file mode 100644
index 00000000000..3479fb7a351
--- /dev/null
+++ b/tests/queries/0_stateless/01497_extract_all_groups_empty_match.reference
@@ -0,0 +1,2 @@
+[[''],[''],[''],[''],[''],[''],['']]
+[['','','','','','','']]
diff --git a/tests/queries/0_stateless/01497_extract_all_groups_empty_match.sql b/tests/queries/0_stateless/01497_extract_all_groups_empty_match.sql
new file mode 100644
index 00000000000..1c4dafd9e2e
--- /dev/null
+++ b/tests/queries/0_stateless/01497_extract_all_groups_empty_match.sql
@@ -0,0 +1,2 @@
+SELECT extractAllGroupsVertical('@#$%^&*', '(\w*)');
+SELECT extractAllGroupsHorizontal('@#$%^&*', '(\w*)');