cleanup: prepare "update_handler" for WITHOUT OVERLAPS

* rename to a generic name
* move remaning initializations from query exec to prepare time
* simplify/unify key handling in open_table_from_share and delayed
* remove dead code
* move tests where they belong

Author: vuvova

mysql-test/main/long_unique.result

@@ -1492,13 +1492,4 @@ DROP TABLE t1, t2;
 #
 CREATE TABLE t1 (pk INT, a TEXT NOT NULL DEFAULT '', PRIMARY KEY (pk), b INT AUTO_INCREMENT, UNIQUE(b), UNIQUE (a,b)) ENGINE=myisam;
 ERROR HY000: AUTO_INCREMENT column `b` cannot be used in the UNIQUE index `a`
-#
-# MDEV-21819 Assertion `inited == NONE || update_handler != this'
-# failed in handler::ha_write_row
-#
-CREATE OR REPLACE TABLE t1 (a INT, b BLOB, s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(b)) ENGINE=MyISAM PARTITION BY HASH(a) PARTITIONS 2;
-INSERT INTO t1 VALUES (1,'foo','2022-01-01', '2025-01-01');
-DELETE FROM t1 FOR PORTION OF app FROM '2023-01-01' TO '2024-01-01';
-ERROR 23000: Duplicate entry 'foo' for key 'b'
-DROP TABLE t1;
 set @@GLOBAL.max_allowed_packet= @allowed_packet;

mysql-test/main/long_unique.test

@@ -573,16 +573,5 @@ DROP TABLE t1, t2;
 --error ER_NO_AUTOINCREMENT_WITH_UNIQUE
 CREATE TABLE t1 (pk INT, a TEXT NOT NULL DEFAULT '', PRIMARY KEY (pk), b INT AUTO_INCREMENT, UNIQUE(b), UNIQUE (a,b)) ENGINE=myisam;
 
---echo #
---echo # MDEV-21819 Assertion `inited == NONE || update_handler != this'
---echo # failed in handler::ha_write_row
---echo #
-
-CREATE OR REPLACE TABLE t1 (a INT, b BLOB, s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(b)) ENGINE=MyISAM PARTITION BY HASH(a) PARTITIONS 2;
-INSERT INTO t1 VALUES (1,'foo','2022-01-01', '2025-01-01');
---error ER_DUP_ENTRY
-DELETE FROM t1 FOR PORTION OF app FROM '2023-01-01' TO '2024-01-01';
-DROP TABLE t1;
-
 # Cleanup
 set @@GLOBAL.max_allowed_packet= @allowed_packet;

mysql-test/suite/period/r/long_unique.result

@@ -0,0 +1,17 @@
+#
+# Assertion `inited == NONE || update_handler != this' failed in
+# handler::ha_write_row
+#
+CREATE TABLE t1 (f VARCHAR(4096), s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(f)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('foo', '2023-08-30', '2025-07-09'),('bar', '2021-01-01', '2021-12-31');
+DELETE FROM t1 FOR PORTION OF app FROM '2023-08-29' TO '2025-07-01';
+DROP TABLE t1;
+#
+# MDEV-21819 Assertion `inited == NONE || update_handler != this'
+# failed in handler::ha_write_row
+#
+CREATE OR REPLACE TABLE t1 (a INT, b BLOB, s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(b)) ENGINE=MyISAM PARTITION BY HASH(a) PARTITIONS 2;
+INSERT INTO t1 VALUES (1,'foo','2022-01-01', '2025-01-01');
+DELETE FROM t1 FOR PORTION OF app FROM '2023-01-01' TO '2024-01-01';
+ERROR 23000: Duplicate entry 'foo' for key 'b'
+DROP TABLE t1;

mysql-test/suite/period/t/long_unique.test

@@ -0,0 +1,23 @@
+--source include/have_partition.inc
+
+--echo #
+--echo # Assertion `inited == NONE || update_handler != this' failed in
+--echo # handler::ha_write_row
+--echo #
+
+CREATE TABLE t1 (f VARCHAR(4096), s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(f)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('foo', '2023-08-30', '2025-07-09'),('bar', '2021-01-01', '2021-12-31');
+DELETE FROM t1 FOR PORTION OF app FROM '2023-08-29' TO '2025-07-01';
+DROP TABLE t1;
+
+--echo #
+--echo # MDEV-21819 Assertion `inited == NONE || update_handler != this'
+--echo # failed in handler::ha_write_row
+--echo #
+
+CREATE OR REPLACE TABLE t1 (a INT, b BLOB, s DATE, e DATE, PERIOD FOR app(s,e), UNIQUE(b)) ENGINE=MyISAM PARTITION BY HASH(a) PARTITIONS 2;
+INSERT INTO t1 VALUES (1,'foo','2022-01-01', '2025-01-01');
+--error ER_DUP_ENTRY
+DELETE FROM t1 FOR PORTION OF app FROM '2023-01-01' TO '2024-01-01';
+DROP TABLE t1;
+

mysql-test/suite/versioning/r/long_unique.result

@@ -4352,16 +4352,6 @@ int ha_partition::write_row(const uchar * buf)
   }
   m_last_part= part_id;
   DBUG_PRINT("info", ("Insert in partition %u", part_id));
-  /*
-    We have to call prepare_for_insert() if we have an update handler
-    in the underlying table (to clone the handler). This is because for
-    INSERT's prepare_for_insert() is only called for the main table,
-    not for all partitions. This is to reduce the huge overhead of cloning
-    a possible not needed handler if there are many partitions.
-  */
-  if (table->s->long_unique_table &&
-      m_file[part_id]->update_handler == m_file[part_id] && inited == RND)
-    m_file[part_id]->prepare_for_insert(0);
 
   start_part_bulk_insert(thd, part_id);
 
@@ -9940,8 +9930,13 @@ void ha_partition::print_error(int error, myf errflag)
     /* fall through to generic error handling. */
   }
 
-  /* In case m_file has not been initialized, like in bug#42438 */
-  if (m_file)
+  /*
+    We choose a main handler's print_error if:
+    * m_file has not been initialized, like in bug#42438
+    * lookup_errkey is set, which means that an error has occured in the
+      main handler, not in individual partitions
+  */
+  if (m_file && lookup_errkey == (uint)-1)
   {
     if (m_last_part >= m_tot_parts)
     {