This bug caused crashes of the server when processing queries with table
value constructors (TVC) that contained subqueries and were used itself as
subselects. For such TVCs the following transformation is applied at the
prepare stage:
VALUES (v1), ... (vn) => SELECT * FROM (VALUES (v1), ... (vn)) tvc_x.
This transformation allows to reduce the problem of evaluation of TVCs used
as subselects to the problem of evaluation of regular subselects.
The transformation is implemented in the wrap_tvc(). The code the function
to mimic the behaviour of the parser when processing the result of the
transformation. However this imitation was not free of some flaws. First
the function called the method exclude() that completely destroyed the
select tree structures below the transformed TVC. Second the function
used the procedure mysql_new_select to create st_select_lex nodes for
both wrapping select of the transformation and TVC. This also led to
constructing of invalid select tree structures.
The patch actually re-engineers the code of wrap_tvc().
Approved by Oleksandr Byelkin <sanja@mariadb.com>
on used subqueries
If a query was based on a table value constructor that contained subqueries
then EXPLAIN for such query did not contain any lines explaining the
execution plans of the subqueries.
This happened because
- no optimize() method was called for any subquery used by the table value
constructor when EXPLAIN command for the query was processed;
- EXPLAIN node created for the table value constructor itself did not
assume that some child nodes could be attached to it.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
of two table value costructors
This bug affected queries with a [NOT] IN/ANY/ALL subquery whose top level
unit contained several table value constructors.
The problem appeared because the code of the function
Item_subselect::fix_fields() that was responsible for wrapping table
value constructors encountered at the top level unit of a [NOT] IN/ANY/ALL
subquery did not take into account that the chain of the select objects
comprising the unit were not immutable.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
This patch actually fixes the bug MDEV-24675 and the bug MDEV-24618:
Assertion failure when TVC uses a row in the context expecting scalar value
The cause of these bugs is the same wrong call of the function that fixes
value expressions in the value list of a table value constructor.
The assertion failure happened when an expression in the value list is of
the row type. In this case an error message was expected, but it was not
issued because the function fix_fields_if_needed() was called for to
check fields of value expressions in a TVC instead of the function
fix_fields_if_needed_for_scalar() that would also check that the value
expressions are are of a scalar type.
The first bug happened when a table value expression used an expression
returned by single-row subselect. In this case the call of the
fix_fields_if_needed_for_scalar virtual function must be provided with
and address to which the single-row subselect has to be attached.
Test cases were added for each of the bugs.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
Allow materialization strategy when collations on the
inner and outer sides of an IN subquery are the same and the
character set of the inner side is a proper subset of the character
set on the outer side.
This allows conversion from utf8mb3 to utf8mb4
as the former is a subset of the later.
This is only allowed when IN predicate is converted to an IN subquery
Backported part of the patch (d6a00d9b18) of MDEV-17905.
1. Code simplification:
Item_default_value handled all these values:
a. DEFAULT(field)
b. DEFAULT
c. IGNORE
and had various conditions to distinguish (a) from (b) and from (c).
Introducing a new abstract class Item_contextually_typed_value_specification,
to handle (b) and (c), so the hierarchy now looks as follows:
Item
Item_result_field
Item_ident
Item_field
Item_default_value - DEFAULT(field)
Item_contextually_typed_value_specification
Item_default_specification - DEFAULT
Item_ignore_specification - IGNORE
2. Introducing a new virtual method is_evaluable_expression() to
determine if an Item is:
- a normal expression, so its val_xxx()/get_date() methods can be called
- or a just an expression substitute, whose value methods cannot be called.
3. Disallowing Items that are not evalualble expressions in table value
constructors.
query with VALUES()
A table value constructor can be used in all contexts where a select
can be used. In particular an ORDER BY clause or a LIMIT clause or both
of them can be attached to a table value constructor to produce a new
query. Unfortunately execution of such queries was not supported.
This patch fixes the problem.
in Field_iterator_table::create_item
When IN predicate is converted to IN subquery we have to ensure that
any item from the select list of the subquery has some name and this name
is unique across the select list.
This was not guaranteed by the code before the patch for MDEV-17222.
If the name of an item of the select list was not set, and this happened
for binary constants, then the server crashed. If the first row in the IN
list contained the same constant in two different positions then the server
returned an error message.
This was fixed by providing all constants in the first row of the IN list
with generated names.
elements of BIGINT or YEAR type in the IN list reaches in_predicate_conversion_threshold
The bug appears at the prepare stage when IN-predicate with the long list
of values is converted into IN-subquery. It happens because values in the
right operand of the IN-predicate that have BIGINT or YEAR types are converted
into the Item_int_with_ref.
To fix it in the procedure Item_func_in::create_value_list_for_tvc
real_item() is taken for each value in the right operand of the IN-predicate.
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
Conversion of NOT IN predicates into NOT IN subqueries did not work
correctly: the predicates actually were converted into IN subqueries.
As a result if the conversion was applied for the query with
a NOT IN predicate the query could return a wrong result set.
As a result of this merge the code for the following tasks appears in 10.3:
- MDEV-12172 Implement tables specified by table value constructors
- MDEV-12176 Transform [NOT] IN predicate with long list of values INTO
[NOT] IN subquery.
TVC can be used in UNION-statement, in view and in subquery.
Files where TVC is defined and its methods are stored added.
Methods exec and prepare for TVC added.
Tests for TVC added.
