From 495d96709fb0b116dbac253bdf0a3c0b12bf775a Mon Sep 17 00:00:00 2001
From: Yuchen Pei <ycp@mariadb.com>
Date: Tue, 15 Apr 2025 11:17:57 +1000
Subject: [PATCH] MDEV-35866 CHECK TABLE get number of rows without
 HA_STATS_RECORDS_IS_EXACT

Call ha_rnd_init followed by two ha_rnd_next's to find whether there
is more than one row.
---
 mysql-test/suite/sql_sequence/check.result | 26 +++++++++++++++++
 mysql-test/suite/sql_sequence/check.test   | 33 ++++++++++++++++++++++
 sql/ha_sequence.cc                         | 26 +++++++++++++++--
 3 files changed, 83 insertions(+), 2 deletions(-)

diff --git a/mysql-test/suite/sql_sequence/check.result b/mysql-test/suite/sql_sequence/check.result
index 2bf644f022c..9439bd5ff22 100644
--- a/mysql-test/suite/sql_sequence/check.result
+++ b/mysql-test/suite/sql_sequence/check.result
@@ -115,3 +115,29 @@ create sequence s;
 update s set minimum_value=500, maximum_value=200;
 ERROR HY000: Storage engine SEQUENCE of the table `test`.`s` doesn't have this option
 drop sequence s;
+#
+# MDEV-35866 mariadb-check does not return warning for incorrect sequence with engine InnoDB
+#
+CREATE SEQUENCE s engine=innodb;
+ALTER TABLE s sequence=0;
+delete from s;
+FLUSH TABLES;
+CHECK TABLE s;
+Table	Op	Msg_type	Msg_text
+test.s	check	Error	Fewer than one row in the table
+test.s	check	error	Corrupt
+DROP SEQUENCE s;
+CREATE SEQUENCE s engine=innodb;
+CHECK TABLE s;
+Table	Op	Msg_type	Msg_text
+test.s	check	status	OK
+DROP SEQUENCE s;
+CREATE SEQUENCE s engine=innodb;
+ALTER TABLE s sequence=0;
+insert into s values (2,1,9223372036854775806,1,1,1000,0,0);
+FLUSH TABLES;
+CHECK TABLE s;
+Table	Op	Msg_type	Msg_text
+test.s	check	Warning	More than one row in the table
+test.s	check	status	OK
+DROP SEQUENCE s;
diff --git a/mysql-test/suite/sql_sequence/check.test b/mysql-test/suite/sql_sequence/check.test
index 2d88478d663..04e48a44ddf 100644
--- a/mysql-test/suite/sql_sequence/check.test
+++ b/mysql-test/suite/sql_sequence/check.test
@@ -137,3 +137,36 @@ create sequence s;
 --error ER_ILLEGAL_HA
 update s set minimum_value=500, maximum_value=200;
 drop sequence s;
+
+--echo #
+--echo # MDEV-35866 mariadb-check does not return warning for incorrect sequence with engine InnoDB
+--echo #
+--source include/have_innodb.inc
+# Fewer than one row
+let $datadir=`select @@datadir`;
+CREATE SEQUENCE s engine=innodb;
+copy_file $datadir/test/s.frm $datadir/test/s1.frm;
+ALTER TABLE s sequence=0;
+delete from s;
+FLUSH TABLES;
+remove_file $datadir/test/s.frm;
+move_file $datadir/test/s1.frm $datadir/test/s.frm;
+CHECK TABLE s;
+DROP SEQUENCE s;
+
+# Just one row, check ok
+CREATE SEQUENCE s engine=innodb;
+CHECK TABLE s;
+DROP SEQUENCE s;
+
+# More than one row
+let $datadir=`select @@datadir`;
+CREATE SEQUENCE s engine=innodb;
+copy_file $datadir/test/s.frm $datadir/test/s1.frm;
+ALTER TABLE s sequence=0;
+insert into s values (2,1,9223372036854775806,1,1,1000,0,0);
+FLUSH TABLES;
+remove_file $datadir/test/s.frm;
+move_file $datadir/test/s1.frm $datadir/test/s.frm;
+CHECK TABLE s;
+DROP SEQUENCE s;
diff --git a/sql/ha_sequence.cc b/sql/ha_sequence.cc
index e2cf7a8c3b1..038d7de80c1 100644
--- a/sql/ha_sequence.cc
+++ b/sql/ha_sequence.cc
@@ -422,10 +422,11 @@ void ha_sequence::print_error(int error, myf errflag)
 
 int ha_sequence::check(THD* thd, HA_CHECK_OPT* check_opt)
 {
+  int error= 0;
   DBUG_ENTER("ha_sequence::check");
   /* Check the underlying engine */
-  if (int ret= file->check(thd, check_opt))
-    DBUG_RETURN(ret);
+  if ((error= file->check(thd, check_opt)))
+    DBUG_RETURN(error);
   /* Check number of rows */
   if ((file->table_flags() & HA_STATS_RECORDS_IS_EXACT))
   {
@@ -439,6 +440,27 @@ int ha_sequence::check(THD* thd, HA_CHECK_OPT* check_opt)
       DBUG_RETURN(HA_ADMIN_CORRUPT);
     }
   }
+  else
+  {
+    if (file->ha_rnd_init_with_error(1))
+      DBUG_RETURN(HA_ADMIN_FAILED);
+    if ((error= file->ha_rnd_next(table->record[0])))
+    {
+      file->ha_rnd_end();
+      if (error == HA_ERR_END_OF_FILE)
+      {
+        my_error(ER_SEQUENCE_TABLE_HAS_TOO_FEW_ROWS, MYF(0));
+        DBUG_RETURN(HA_ADMIN_CORRUPT);
+      }
+      file->print_error(error, MYF(0));
+      DBUG_RETURN(HA_ADMIN_FAILED);
+    }
+    if (!file->ha_rnd_next(table->record[0]))
+      push_warning(thd, Sql_condition::WARN_LEVEL_WARN,
+                   ER_SEQUENCE_TABLE_HAS_TOO_MANY_ROWS,
+                   ER_THD(thd, ER_SEQUENCE_TABLE_HAS_TOO_MANY_ROWS));
+    file->ha_rnd_end();
+  }
   /*
     Initialise the sequence from the table if needed.
   */