The function st_select_lex_unit::exec_recursive() missed resetting of
select_limit_cnt and offset_limit_cnt before execution of union parts.
As a result recursive CTEs specified by UNIONs whose SELECTs contained
LIMIT/OFFSET could return wrong sets of records.
This problem manifested itself when a join query used two or more
materialized CTE such that each of them employed the same recursive CTE.
The bug caused a crash. The crash happened because the cleanup()
function was performed premature for recursive CTE. This clean up was
induced by the cleanup of the first CTE referenced the recusrsive CTE.
This cleanup destroyed the structures that would allow to read from the
temporary table containing the rows of the recursive CTE and an attempt to read
these rows for the second CTE referencing the recursive CTE triggered a
crash.
The clean up for a recursive CTE R should be performed after the cleanup
of the last materialized CTE that uses R.
value constructor shows wrong number of rows
If the specification of a derived table contained a table value constructor
then the optimizer incorrectly estimated the number of rows in the derived
table. This happened because the optimizer did not take into account the
number of rows in the constructor. The wrong estimate could lead to choosing
inefficient execution plans.
This is to mark that a field is indirectly part of a key, which simplifes
checking if we need to have this field up to date to evaluate a key.
For example:
CREATE TABLE t1 (a int, b int as (a) virtual,
c int as (b) virtual, index(c))
would mark a and b with PART_INDIRECT_KEY_FLAG.
c is marked with PART_KEY_FLAG as before.
This bug caused crashes for queries with unreferenced non-recursive
CTEs specified by unions.It happened because the function
st_select_lex_unit::prepare() tried to use the value of the field 'derived'
that could not be set for unferenced CTEs as there was no derived
table associated with an unreferenced CTE.
The current code does not support recursive CTEs whose specifications
contain a mix of ALL UNION and DISTINCT UNION operations.
This patch catches such specifications and reports errors for them.
with recursive subquery
There were two problems:
1. The code did not report that usage of global ORDER BY / LIMIT clauses
was not supported yet.
2. The code just reset fake_select_lex of the the unit specifying
a recursive CTE to NULL and that caused memory leaks in some cases.
In this issue we hit the assert because we are adding addition fields to the field JOIN::all_fields list. This
is done because HEAP tables can't index BIT fields so we need to use an additional hidden field for grouping because later it will be
converted to a LONG field. Original field will remain of the BIT type and will be returned. This happens when we convert DISTINCT to
GROUP BY.
The solution is to take into account the number of such hidden fields that would be added to the field
JOIN::all_fields list while calculating the size of the ref_pointer_array.
Partition engine FT keys are implemented in such a way that
the FT function's cleanup() methods use table's internals.
So calling them after close_thread_tables is unsafe.
Forced columns of recursive CTEs to be nullable. SQL standard
requires this only from recursive columns, but in our code
so far we do not differentiate between recursive and non-recursive
columns when aggregating types of the union that specifies a
recursive CTE.
Make sure that SELECT_LEX_UNIT::derived, behaves as documented
(points to the "TABLE_LIST representing this union in the
embedding select"). For recursive CTE this was not necessarily
the case, it could've pointed to the TABLE_LIST inside the CTE,
not in the embedding select.
To fix:
* don't update unit->derived in mysql_derived_prepare(), pass derived
as an argument to st_select_lex_unit::prepare()
* prefer to set unit->derived in TABLE_LIST::init_derived()
to the TABLE_LIST in the embedding select, not to the recursive
reference. Fail if there are many TABLE_LISTs in the embedding
select with conflicting FOR SYSTEM_TIME clauses.
cleanup:
* remove redundant THD* argument from st_select_lex_unit::prepare()
This bug happened due to a defect of the implementation of the handler
function ha_delete_all_rows() for the ARIA engine.
The function maria_delete_all_rows() truncated the table, but it didn't
touch the write cache, so the cache's write offset was not reset.
In the scenario like in the function st_select_lex_unit::exec_recursive
when first all records were deleted from the table and then several new
records were added some metadata became inconsistent with the state of
the cache. As a result the table scan function could not read records
at the end of the table.
The same defect could be found in the implementation of ha_delete_all_rows()
for the MYISAM engine mi_delete_all_rows().
Additionally made late instantiation for the temporary table used to store
rows that were used for each new iteration when executing a recursive CTE.
the non-recursive CTE defined with UNION
The problem appears as the columns of the non-recursive CTE weren't renamed.
The renaming procedure was called for recursive CTEs only.
To fix it in the procedure st_select_lex_unit::prepare
With_element::rename_columns_of_derived_unit is called now for both CTEs:
recursive and non-recursive.
is not supported
Allowed to use recursive references in derived tables.
As a result usage of recursive references in operands of
INTERSECT / EXCEPT is now supported.
This was done in, among other things:
- thd->db and thd->db_length
- TABLE_LIST tablename, db, alias and schema_name
- Audit plugin database name
- lex->db
- All db and table names in Alter_table_ctx
- st_select_lex db
Other things:
- Changed a lot of functions to take const LEX_CSTRING* as argument
for db, table_name and alias. See init_one_table() as an example.
- Changed some function arguments from LEX_CSTRING to const LEX_CSTRING
- Changed some lists from LEX_STRING to LEX_CSTRING
- threads_mysql.result changed because process list_db wasn't always
correctly updated
- New append_identifier() function that takes LEX_CSTRING* as arguments
- Added new element tmp_buff to Alter_table_ctx to separate temp name
handling from temporary space
- Ensure we store the length after my_casedn_str() of table/db names
- Removed not used version of rename_table_in_stat_tables()
- Changed Natural_join_column::table_name and db_name() to never return
NULL (used for print)
- thd->get_db() now returns db as a printable string (thd->db.str or "")
TRASH was mapped to TRASH_FREE and was supposed to be used for memory
that should not be accessed anymore, while TRASH_ALLOC() is to be
used for uninitialized but to-be-used memory.
But sometimes TRASH() was used in the latter sense.
Remove TRASH() macro, always use explicit TRASH_ALLOC() or TRASH_FREE().
with recursive reference in subquery
If a recursive CTE uses a subquery with recursive reference then
the virtual function reset() must be called after each iteration
performed at the execution of the CTE.
Most "new" failures fixed in the following files:
- sql_select.cc
- item.cc
- item_func.cc
- opt_subselect.cc
Other things:
- Allocate udf_handler strings in mem_root
- Required changes in sql_string.h
- Add mem_root as argument to some new [] calls
- Mark udf_handler strings as thread specific
- Removed some comment blocks with code
With INTERSECT/EXCEPT fact that subquery item of IN/ALL/ANY was not assigned value does not mean that temporary table used for calculating unit is empty (records could be deleted).
