> ------------------------------------------------------------
> revno: 3520
> revision-id: sergey.glukhov@oracle.com-20101214093303-wmo9mqcb8rz0wv9f
> parent: tor.didriksen@oracle.com-20101213161301-81lprlbune7r98dl
> committer: Sergey Glukhov <sergey.glukhov@oracle.com>
> branch nick: mysql-5.1-bugteam
> timestamp: Tue 2010-12-14 12:33:03 +0300
> message:
>   Fixed following problems:
>   --Bug#52157 various crashes and assertions with multi-table update, stored function
>   --Bug#54475 improper error handling causes cascading crashing failures in innodb/ndb
>   --Bug#57703 create view cause Assertion failed: 0, file .\item_subselect.cc, line 846
>   --Bug#57352 valgrind warnings when creating view
>   --Recently discovered problem when a nested materialized derived table is used
>     before being populated and it leads to incorrect result
>   
>   We have several modes when we should disable subquery evaluation.
>   The reasons for disabling are different. It could be
>   uselessness of the evaluation as in case of 'CREATE VIEW'
>   or 'PREPARE stmt', or we should disable subquery evaluation
>   if tables are not locked yet as it happens in bug#54475, or
>   too early evaluation of subqueries can lead to wrong result
>   as it happened in Bug#19077.
>   Main problem is that if subquery items are treated as const
>   they are evaluated in ::fix_fields(), ::fix_length_and_dec()
>   of the parental items as a lot of these methods have
>   Item::val_...() calls inside.
>   We have to make subqueries non-const to prevent unnecessary
>   subquery evaluation. At the moment we have different methods
>   for this. Here is a list of these modes:
>   
>   1. PREPARE stmt;
>   We use UNCACHEABLE_PREPARE flag.
>   It is set during parsing in sql_parse.cc, mysql_new_select() for
>   each SELECT_LEX object and cleared at the end of PREPARE in
>   sql_prepare.cc, init_stmt_after_parse(). If this flag is set
>   subquery becomes non-const and evaluation does not happen.
>   
>   2. CREATE|ALTER VIEW, SHOW CREATE VIEW, I_S tables which
>      process FRM files
>   We use LEX::view_prepare_mode field. We set it before
>   view preparation and check this flag in
>   ::fix_fields(), ::fix_length_and_dec().
>   Some bugs are fixed using this approach,
>   some are not(Bug#57352, Bug#57703). The problem here is
>   that we have a lot of ::fix_fields(), ::fix_length_and_dec()
>   where we use Item::val_...() calls for const items.
>   
>   3. Derived tables with subquery = wrong result(Bug19077)
>   The reason of this bug is too early subquery evaluation.
>   It was fixed by adding Item::with_subselect field
>   The check of this field in appropriate places prevents
>   const item evaluation if the item have subquery.
>   The fix for Bug19077 fixes only the problem with
>   convert_constant_item() function and does not cover
>   other places(::fix_fields(), ::fix_length_and_dec() again)
>   where subqueries could be evaluated.
>   
>   Example:
>   CREATE TABLE t1 (i INT, j BIGINT);
>   INSERT INTO t1 VALUES (1, 2), (2, 2), (3, 2);
>   SELECT * FROM (SELECT MIN(i) FROM t1
>   WHERE j = SUBSTRING('12', (SELECT * FROM (SELECT MIN(j) FROM t1) t2))) t3;
>   DROP TABLE t1;
>   
>   4. Derived tables with subquery where subquery
>      is evaluated before table locking(Bug#54475, Bug#52157)
>   
>   Suggested solution is following:
>   
>   -Introduce new field LEX::context_analysis_only with the following
>    possible flags:
>    #define CONTEXT_ANALYSIS_ONLY_PREPARE 1
>    #define CONTEXT_ANALYSIS_ONLY_VIEW    2
>    #define CONTEXT_ANALYSIS_ONLY_DERIVED 4
>   -Set/clean these flags when we perform
>    context analysis operation
>   -Item_subselect::const_item() returns
>    result depending on LEX::context_analysis_only.
>    If context_analysis_only is set then we return
>    FALSE that means that subquery is non-const.
>    As all subquery types are wrapped by Item_subselect
>    it allow as to make subquery non-const when
>    it's necessary.