From 5655a2f8ae315c79c138b11d065eb1c8867d0962 Mon Sep 17 00:00:00 2001
From: PranavKTiwari <pranav.tiwari@mariadb.com>
Date: Mon, 15 Jun 2026 15:27:50 +0530
Subject: [PATCH] MDEV-30297 Server crash / assertion failure in
 Compare_identifiers::operator upon dropping period with empty name
 Lex_cstring_with_compare::streq() could invoke Compare_identifiers on
 default-constructed Lex_cstring objects (str == NULL, length == 0).
 Compare_identifiers assumes non-null strings and asserts in debug builds or
 crashes in non-debug builds. Guard against null string pointers in streq()
 before invoking the comparator.

---
 mysql-test/suite/period/r/alter.result |  9 +++++++++
 mysql-test/suite/period/t/alter.test   | 10 ++++++++++
 sql/vers_string.h                      |  6 +++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/mysql-test/suite/period/r/alter.result b/mysql-test/suite/period/r/alter.result
index 9eb4555c0bdad..0d82acb994449 100644
--- a/mysql-test/suite/period/r/alter.result
+++ b/mysql-test/suite/period/r/alter.result
@@ -222,3 +222,12 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
 drop table t1;
 # End of 10.5 tests
+#
+# MDEV-30297 Server crash / assertion failure in Compare_identifiers::operator upon dropping period with empty name
+#
+create table t (a int);
+alter table t drop period if exists for ``;
+Warnings:
+Note	1091	Can't DROP PERIOD ``; check that it exists
+drop table t;
+# End of 10.11 tests
diff --git a/mysql-test/suite/period/t/alter.test b/mysql-test/suite/period/t/alter.test
index fab933eca879c..24f61ab223695 100644
--- a/mysql-test/suite/period/t/alter.test
+++ b/mysql-test/suite/period/t/alter.test
@@ -190,3 +190,13 @@ show create table t1;
 drop table t1;
 
 --echo # End of 10.5 tests
+
+--echo #
+--echo # MDEV-30297 Server crash / assertion failure in Compare_identifiers::operator upon dropping period with empty name
+--echo #
+create table t (a int);
+alter table t drop period if exists for ``;
+
+drop table t;
+
+--echo # End of 10.11 tests
diff --git a/sql/vers_string.h b/sql/vers_string.h
index 9c1730fad81a5..d91b2538d10b5 100644
--- a/sql/vers_string.h
+++ b/sql/vers_string.h
@@ -66,7 +66,11 @@ struct Lex_cstring_with_compare : public Lex_cstring
   { }
   bool streq(const Lex_cstring_with_compare& b) const
   {
-    return Lex_cstring::length == b.length && 0 == Compare()(*this, b);
+    if (length != b.length)
+      return false;
+    if (str == NULL || b.str == NULL)
+      return str == b.str;
+    return length == 0 || 0 == Compare()(*this, b);
   }
   operator const char* () const
   {