The problem resided in Item_window_func implementation,
and it was revealed by bb-10.2-ext specific changes:

Item_window_func::save_in_field() works differently in bb-10.2-ext vs 10.2:

- 10.2 goes through val_str()
- bb-10.2-ext goes through get_date(), due to Type_handler related changes.
  get_date() tries to convert empty string to DATETIME, hence the warning.

During a discussion with Vicentiu, it was decided to fix
Item_window_func::val_xxx() to return NULL
(instead of an "empty" value, such as 0 for numbers and '' for strings)
when force_return_blank is set.

1. The "sf_tail" rule had a lot of rules with part markers, e.g:

     /* $1 */

They make the grammar really hard to read.
Removing all these markers.

2. Moving the RETURNS clause into a separate sp_return_type rule,
to make sf_tail even more simpler. Note, sp_return_type will be needed
soon for packages anyway.

The code in mysql_execute_command() for SQLCOM_CREATE_DB, SQLCOM_DROP_DB
and SQLCOM_ALTER_DB contained around 20 lines of similar code.
Moving this code into a new function prepare_db_action().

When it comes to DEFAULT values of columns, InnoDB is imposing both
unnecessary and insufficient conditions on whether ALGORITHM=INPLACE
should be allowed for ALTER TABLE.

When changing an existing column to NOT NULL, any NULL values in the
columns only get a special treatment if the column is changed to an
AUTO_INCREMENT column (which is not supported by ALGORITHM=INPLACE)
or the column type is TIMESTAMP. In all other cases, an error
must be reported for the failure to convert a NULL value to NOT NULL.

InnoDB was unnecessarily interested in whether the DEFAULT value
is not constant when altering other than TIMESTAMP columns. Also,
when changing a TIMESTAMP column to NOT NULL, InnoDB was performing
an insufficient check, and it was incorrectly allowing a constant
DEFAULT value while not being able to replace NULL values with that
constant value.

Furthermore, in ADD COLUMN, InnoDB is unnecessarily rejecting certain
nondeterministic DEFAULT expressions (depending on the session
parameters or the current time).

This patch corrects the fix for mdev-12845.

Merged relevant part of MySQL revision:
https://github.com/mysql/mysql-server/commit/565d20b44f24fcc855dc616164d87b03cfad10bc

Relaxed assertion (in MySQL it was removed).
For "LOCK TABLES t1 WRITE CONCURRENT, t1 READ" upgrade lock to weakest
existing suitable lock, which is MDL_SHARED_NO_READ_WRITE.

buf_flush_page_cleaner_coordinator(): Signal the thread creator
that the error log output regarding setpriority() has been issued.

innobase_start_or_create_for_mysql(): Wait for
buf_flush_page_cleaner_coordinator() to completely start up.

This prevents sporadic failures of tests that search the server
error log for InnoDB redo log recovery messages.

While the primary purpose of innodb_force_recovery is to allow
data to be rescued from an InnoDB instance that would crash due
to some data corruption, the settings 1, 2, or 3 are relatively
safe to use and there is no need to prevent write transactions
in these modes.

The setting innodb_force_recovery=4 and above can cause database
corruption. For those modes, we already set the flag
high_level_read_only to disable modifications, except DROP TABLE.

MODIFICATIONS_NOT_ALLOWED_MSG_FORCE_RECOVERY: Remove. There is no
need to spam the error log for each refused DML operation. It suffices
to return an error to the client. There will be messages at startup
if innodb_read_only or innodb_force_recovery are preventing writes.

This patch fills in a serious flaw in the
code that supports condition pushdown into
materialized views / derived tables.

If a predicate happened to contain a reference
to a mergeable view / derived table and it does
not depended directly on the target materialized
view / derived table then the predicate was not
considered as a subject to pusdown to this view
/ derived table.

If no checkpoint information is present, do not write to the data files.
These writes would violate innodb_read_only=ON, among other things.

The original intention of the setting innodb_force_recovery=3 was to
disable background activity that could create trouble, most notably,
the rollback of incomplete transactions, and the purge of transaction
history.

MySQL 5.6 introduced more background threads, it is creating
dict_stats_thread and fts_optimize_thread even though these threads
are at least as non-essential as the rollback and purge. These
threads are in fact worse, because they can create new transactions
on their own.

innobase_start_or_create_for_mysql(): Do not create any internal
undo log sources unless innodb_force_recovery<3.

Parameters can be MYSQL_TYPE_VARCHAR for long data load.

These errors should only be possible when bootstrap is aborted
and restarted.

buf_flush_init_for_writing(): Reset the FIL_PAGE_TYPE
of the TRX_SYS page to the canonical value
FIL_PAGE_TYPE_TRX_SYS instead of FIL_PAGE_TYPE_UNKNOWN.

When running setup fields during the final step of insert using select
the final setup_fields does not have any sum functions. Our current
condition for calling split_sum_func however would attempt to use an empty
NULL sum_func_list, if the item contained a window function.

The solution is to not perform another split_sum_func for the item
containing a window function if we do not actually have a sum_func_list.

This will also change the minimum and maximum value of
innodb_log_file_size to 1MiB and 512GiB, respectively.

MDEV-12975 InnoDB redo log minimum size check uses detected file size instead of requested innodb_log_file_size

log_calc_max_ages(): Use the requested size in the check, instead of
the detected redo log size. The redo log will be resized at startup
if it differs from what has been requested.

The option was basically duplicating InnoDB functionality.
Persistent statistics can be accessed via the tables
mysql.innodb_table_stats and mysql.innodb_index_stats.

These functions cannot possibly work in MariaDB 10.2, and it is
uncertain if they really work in 10.1 either.

Additional tests for MDEV-10309 COALESCE(12345678900) makes a column of a wrong type and truncates the data

This is another attempt to fix the bug mdev-12992.
This patch introduces st_select_lex::context_analysis_place for
the place in SELECT where context analysis is currently performed.
It's similar to st_select_lex::parsing_place, but it is used at
the preparation stage.

             lock not released after timeout

Release GRL if FLUSH TABLES phase failed.

When the btr_search_latch was split into an array of latches
in MySQL 5.7.8 as part of the Oracle Bug#20985298 fix, the "caching"
of the latch across storage engine API calls was removed, and
the field trx->has_search_latch would only be set during a short
time frame in the execution of row_search_mvcc(), which was
formerly called row_search_for_mysql().

This means that the column
INFORMATION_SCHEMA.INNODB_TRX.TRX_ADAPTIVE_HASH_LATCHED will always
report 0. That column cannot be removed in MariaDB 10.2, but it
can be removed in future releases.

trx_t::has_search_latch: Remove.

trx_assert_no_search_latch(): Remove.

row_sel_try_search_shortcut_for_mysql(): Remove a redundant condition
on trx->has_search_latch (it was always true).

sync_check_iterate(): Make the parameter const.

sync_check_functor_t: Make the operator() const, and remove result()
and the virtual destructor. There is no need to have mutable state
in the functors.

sync_checker<bool>: Replaces dict_sync_check and btrsea_sync_check.

sync_check: Replaces btrsea_sync_check.

dict_sync_check: Instantiated from sync_checker.

sync_allowed_latches: Use std::find() directly on the array.
Remove the std::vector.

TrxInInnoDB::enter(), TrxInInnoDB::exit(): Remove obviously redundant
debug assertions on trx->in_depth, and use equality comparison against 0
because it could be more efficient on some architectures.

The sole purpose of handlerton::release_temporary_latches and its wrapper
function was to release the InnoDB adaptive hash index latch
(btr_search_latch).

When the btr_search_latch was split into an array of latches
in MySQL 5.7.8 as part of the Oracle Bug#20985298 fix, the "caching"
of the latch across storage engine API calls was removed. As part of that,
the function trx_search_latch_release_if_reserved() was changed to an
assertion and the function trx_reserve_search_latch_if_not_reserved()
was removed, and handlerton::release_temporary_latches() practically
became a no-op.

Note: MDEV-12121 replaced the function
trx_search_latch_release_if_reserved()
with the more appropriately named macro trx_assert_no_search_latch().

Merge 10.2 into bb-10.2-ext; also, fix MDEV-13015 After restart, InnoDB wrongly thinks that a SEQUENCE is a TABLE

sql_sequence.read_only: Show that the sequence can be read in
both read-only and read-write mode, and that the sequence remains
accessible after a server restart.

dict_sys_tables_type_to_tf(): Change the parameter n_cols to not_redundant.

dict_tf_is_valid_not_redundant(): Refactored from dict_tf_is_valid().

dict_sys_tables_type_valid(): Replaces dict_sys_tables_type_validate().
Use the common function dict_tf_is_valid_not_redundant(), which validates
PAGE_COMPRESSION_LEVEL more strictly.

DICT_TF_GET_UNUSED(flags): Remove.

innodb.table_flags: Adjust the test case. Due to the MDEV-12873 fix
in 10.2, the corrupted flags for table test.td would be converted,
and a tablespace flag mismatch will occur when trying to open the file.