Problem: caseup_multiply and casedn_multiply members
were not initialized for a dynamic collation, so
UPPER() and LOWER() functions returned empty strings.
Fix: initializing the members properly.
Adding tests:
mysql-test/r/ctype_ldml.result
mysql-test/t/ctype_ldml.test
Applying the fix:
mysys/charset.c
(Original patch by Sinisa Milivojevic)
The YEAR(4) value of 2000 was equal to the "bad" YEAR(4) value of 0000.
The get_year_value() function has been modified to not adjust bad
YEAR(4) value to 2000.
The problem is that when we make conditon for
grouped result const part of condition is cut off.
It happens because some parts of 'having' condition
which refer to outer join become const after
make_join_statistics. These parts may be lost
during further having condition transformation
in JOIN::exec. The fix is adding 'having'
condition check for const tables after
make_join_statistics is performed.
This has been back-ported from 6.0 as the problems proved to afflict
5.1 as well.
The fix exposed two new bugs. They were reported as follows.
Bug no 52174: Sometimes wrong plan when reading a MAX value
from non-NULL index
Bug no 52173: Reading NULL value from non-NULL index gives wrong
result in embedded server
Both bugs taken together affect a much smaller class of queries than #47762,
so the fix stays for now.
Optimizer erroneously translated LEFT JOIN into INNER JOIN.
It leads to cutting rows with NULL right side. It happens
because Item_row uses not_null_tables() method form the
base(Item) class and does not calculate 'null tables'
properly. The fix is adding calculation of 'not null tables'
to Item_row.
The crash happens because of discrepancy between values of
conts_tables and join->const_table_map(make_join_statisctics).
Calculation of conts_tables used condition with
HA_STATS_RECORDS_IS_EXACT flag check. Calculation of
join->const_table_map does not use this flag check.
In case of MERGE table without union with index
the table does not become const table and
thus join_read_const_table() is not called
for the table. join->const_table_map supposes
this table is const and later in make_join_select
this table is used for making&calculation const
condition. As table record buffer is not populated
it leads to crash.
The fix is adding a check if an engine supports
HA_STATS_RECORDS_IS_EXACT flag before updating
join->const_table_map.
reverse DNS lookup of "localhost" returns "broadcasthost" on Snow Leopard, and NULL on most others.
Simply ignore the output, as this is not an essential part of UDF testing.
definition at engine
If a single ALTER TABLE contains both DROP INDEX and ADD INDEX using
the same index name (a.k.a. index modification) we need to disable
in-place alter table because we can't ask the storage engine to have
two copies of the index with the same name even temporarily (if we
first do the ADD INDEX and then DROP INDEX) and we can't modify
indexes that are needed by e.g. foreign keys if we first do
DROP INDEX and then ADD INDEX.
Fixed the problem by disabling in-place ALTER TABLE for these cases.
NULL column for NULL
The optimization to read MIN() and MAX() values from an
index did not properly handle comparisons with NULL
values. Fixed by giving up the particular optimization step
if there are non-NULL safe comparisons with NULL values, as
the result is NULL anyway.
Also, Oracle copyright notice was added to all files.
Base Tables
The type inferrence of a view column caused the result to be
interpreted as the wrong type: DATE colums were interpreted
as TIME and TIME as DATETIME. This happened because view
columns are represented by Item_ref objects as opposed to
Item_field's. Item_ref had no method for retrieving a TIME
value and thus was forced to depend on the default
implementation for any expression, which caused the
expression to be evaluated as a string and then parsed into
a TIME/DATETIME value.
Fixed by letting Item_ref classes forward the request for a
TIME value to the referred Item - which is a field in this
case - this reads the TIME value directly without
conversion.
index cardinalities=1
Parallel repair didn't poroperly update index cardinality
in certain cases.
When myisam_sort_buffer_size is not enough to store all
keys, index cardinality was updated before index was
actually written, when no index statistic is available.
(regression)
Problem was that partition pruning did not exclude the
last partition if the range was beyond it
(i.e. not using MAXVALUE)
Fix was to not include the last partition if the
partitioning function value was not within the partition
range.
SET autocommit=1 while XA transaction is active may
cause various side effects, including memory corruption
and server crash.
The problem is that SET autocommit=1 and further queries
attempt to commit local transaction, whereas XA transaction
is still active.
As local and XA transactions are mutually exclusive, this
patch forbids enabling autocommit mode while XA transaction
is active.
The problem was that UNINSTALL PLUGIN wasn't performing privilege
checks before removing a plugin. Any user (including users without
any kind of privileges) could uninstall any plugin.
The solution is to verify if the user has the DELETE privilege for
the mysql.plugin table before uninstalling a plugin.
The problem is that Item_direct_view_ref which is inherited
from Item_ident updates orig_table_name and table_name with
the same values. The fix is introduction of new constructor
into Item_ident and up which updates orig_table_name and
table_name separately.
The problem is that not all column names retrieved from a SELECT
statement can be used as view column names due to length and format
restrictions. The server failed to properly check the conformity
of those automatically generated column names before storing the
final view definition on disk.
Since columns retrieved from a SELECT statement can be anything
ranging from functions to constants values of any format and length,
the solution is to rewrite to a pre-defined format any names that
are not acceptable as a view column name.
The name is rewritten to "Name_exp_%u" where %u translates to the
position of the column. To avoid this conversion scheme, define
explict names for the view columns via the column_list clause.
Also, aliases are now only generated for top level statements.
The problem was that bits of the destructive equality propagation
optimization weren't being undone after the execution of a stored
program. Modifications to the parse tree that are based on transient
properties must be undone to enable the re-execution of stored
programs.
The solution is to cleanup any references to predicates generated
by the equality propagation during the execution of a stored program.
Spatial indexes were not checking for out-of-record condition in
the handler next command when the previous command didn't found
rows.
Fixed by making the rtree index to check for end of rows condition
before re-using the key from the previous search.
Fixed another crash if the tree has changed since the last search.
Added a test case for the other error.
auto_increment on duplicate entry
The bug was that when INSERT_ID was used and the storage
engine was told to release any reserved but not used
auto_increment values, it set the highest auto_increment
value to INSERT_ID.
The fix was to check if the auto_increment value was forced
by user (INSERT_ID) or by slave-thread, i.e. not auto-
generated. So that it is only allowed to release generated
values.
Spatial indexes were not checking for out-of-record condition in
the handler next command when the previous command didn't found
rows.
Fixed by making the rtree index to check for end of rows condition
before re-using the key from the previous search.
Fixed another crash if the tree has changed since the last search.
Added a test case for the other error.
consider clustered primary keys
Choosing a shortest index for the covering index scan,
the optimizer ignored the fact, that the clustered primary
key read involves whole table data.
The find_shortest_key function has been modified to
take into account that fact that a clustered PK has a
longest key of possible covering indices.
Problem was block_size on partitioned tables was not set,
resulting in keys_per_block was not correct which affects
the cost calculation for read time of indexes (including
cost for group min/max).Which resulted in a bad optimizer
decision.
Fixed by setting stats.block_size correctly.
work in 5.1.40)
MERGE engine fails to open child table from a different
database if child table/database name contains characters
that are subject for table name to filename encoding
(WL1324).
Another problem is that MERGE engine didn't properly open
child table from the same database if child table name
contains characters like '/', '#'.
The problem was that table name to file name encoding was
applied inconsistently:
* On CREATE: encode table name + database name if child
table is in different database; do not encode table
name if child table is in the same database;
* No decoding on open.
With this fix child table/database names are always
encoded on CREATE and decoded on open. Compatibility
with older tables preserved.
Along with this patch comes fix for SHOW CREATE TABLE,
which used to show child table/database path instead
of child table/database names.
If an outer query is broken, a subquery might not even get set up.
EXPLAIN EXTENDED did not expect this and merrily tried to de-ref all
of the half-setup info.
We now catch this case and print as much as we have, as it doesn't cost us
anything (doesn't make regular execution slower).
backport from 5.1
insert...select
Queries following bulk insert into an empty MyISAM table
may break it. This was pure MyISAM problem.
When bulk insert into an empty table is complete, MyISAM
may want to enable indexes via repair by sort. If repair
by sort fails (e.g. insufficient buffer), MyISAM failover
to repair with key cache, requesting repair of data file.
Repair of data file performs data file substitution. This
means that current table instance will point to new data
file. Other cached table instances are still pointing to
an old, deleted data file.
This is fixed by not requesting repair of data file
during enable indexes.
Explicit REPAIR is not affected, since it flushes all
table instances.
for same data when using bit fields
Problem: checksum for BIT fields may be computed incorrectly
in some cases due to its storage peculiarity.
Fix: convert a BIT field to a string then calculate its checksum.
The problem was that the CSV storage engine does not support NULL
fields, yet in some early 5.1 version the log tables (general_log
and slow_log) were created with null fields. On top of this, when
altering a CSV table column, all fields of the table must be NOT
NULL otherwise the alteration fails.
The solution is to ensure that during upgrade all columns of the
log tables are NOT NULL.
The problem is that cond->fix_fields(thd, 0) breaks
condition(cuts off 'having'). The reason of that is
that NULL valued Item pointer is present in the
middle of Item list and it breaks the Item processing
loop.
performance degradation.
Filesort + join cache combination is preferred to full index scan because it
is usually faster. But it's not the case when the index is clustered one.
Now test_if_skip_sort_order function prefers filesort only if index isn't
clustered.
Detailed revision comments:
r6538 | sunny | 2010-01-30 00:43:06 +0200 (Sat, 30 Jan 2010) | 6 lines
branches/5.1: Check *first_value every time against the column max
value and set *first_value to next autoinc if it's > col max value.
ie. not rely on what is passed in from MySQL.
[49497] Error 1467 (ER_AUTOINC_READ_FAILED) on inserting a negative value
rb://236
Detailed revision comments:
r6536 | sunny | 2010-01-30 00:13:42 +0200 (Sat, 30 Jan 2010) | 6 lines
branches/5.1: Check *first_value everytime against the column max
value and set *first_value to next autoinc if it's > col max value.
ie. not rely on what is passed in from MySQL.
[49497] Error 1467 (ER_AUTOINC_READ_FAILED) on inserting a negative value
rb://236
Propagation of a large unsigned numeric constant
in the WHERE expression led to wrong result.
For example,
"WHERE a = CAST(0xFFFFFFFFFFFFFFFF AS USIGNED) AND FOO(a)",
where a is an UNSIGNED BIGINT, and FOO() accepts strings,
was transformed to "... AND FOO('-1')".
That has been fixed.
Also EXPLAIN EXTENDED printed incorrect numeric constants in
transformed WHERE expressions like above. That has been
fixed too.
The problem was in an incorrect debug assertion. The expression
used in the failing assertion states that when finding
references matching ORDER BY expressions, there can be only one
reference to a single table. But that does not make any sense,
all test cases for this bug are valid examples with multiple
identical WHERE expressions referencing the same table which
are also present in the ORDER BY list.
Fixed by removing the failing assertion. We also have to take
care of the 'found' counter so that we count multiple
references only once. We rely on this fact later in
eq_ref_table().
When EXPLAIN EXTENDED tries to print column names, it checks whether the
referenced table is CONST (in which case, the column's value rather than
its name will be printed). If no proper table is reference (i.e. because
a derived table was used that has since gone out of scope), this will fail
spectacularly.
This ports an equivalent of the fix for Bug 43354.
CHECK_FIELD_IGNORE was treated as CHECK_FIELD_ERROR_FOR_NULL;
UPDATE...SET...NULL on NOT NULL fields behaved differently after
a trigger.
Now distinguishes between IGNORE and ERROR_FOR_NULL and save/restores
check-field options.
Table corruption happens during table reading in ha_tina::find_current_row() func.
Field::store() method returns error(true) if stored value is 0.
The fix:
added special case for enum type which correctly processes 0 value.
Additional fix:
INSERT...(default) and INSERT...() have the same behaviour now for enum type.
The problem is that during temporary table creation uneven bits
are not taken into account for hidden fields. It leads to incorrect
calculation&allocation of null bytes size for table record. And
if grouped value is null we set wrong bit for this value(see end_update()).
Fixed by adding separate calculation of uneven bit for hidden fields.
This bug is just one facet of stored routines not being able to
detect changes in meta-data (WL#4179). This particular problem
can be triggered within a single session due to the improper
management of the pre-locking list if the view is expanded after
the pre-locking list is calculated.
Since the overall solution for the meta-data detection issue is
planned for a later release, for now a workaround is used to
fix this particular aspect that only involves a single session.
The workaround is to flush the thread-local stored routine cache
every time a view is created or modified, causing locally cached
routines to be re-evaluated upon invocation.
The problem becomes apparent only if HAVE_purify is undefined.
It related to the part of code placed in open_table_from_share() fuction
where we initialize record buffer only if HAVE_purify is enabled.
So in case of HAVE_purify=OFF record buffer is not initialized
on open table stage.
Next we read key, find NULL value and update appropriate null bit
but do not update record buffer. After that the record is stored
in the join cache(store_record_in_cache). For CHAR fields we
strip trailing spaces and in our case this procedure uses
uninitialized record buffer.
The fix is to skip stripping space procedure in case of null values
for CHAR fields(partially based on 6.0 JOIN_CACHE implementation).
removed in MySQL 6.0
CREATE TABLE... TYPE= returns the warning "The syntax
'TYPE=storage_engine' is deprecated and will be removed in
MySQL 6.0. Please use 'ENGINE=storage_engine' instead"
This syntax is deprecated already from version 5.4.4, so
the message has been changed.
In addition, the deprecation macro was changed to reflect
the ServerPT decision not to include version number in the
warning message.
A number of test result files have been changed as a
consequence of the change in the deprecation macro.
Queries optimized with GROUP_MIN_MAX didn't cleanup KEYREAD
optimization properly. As a result subsequent queries may
return incomplete rows (fields are initialized to default
values).
Grouping by a subquery in a query with a distinct aggregate
function lead to a wrong result (wrong and unordered
grouping values).
There are two related problems:
1) The query like this:
SELECT (SELECT t1.a) aa, COUNT(DISTINCT b) c
FROM t1 GROUP BY aa
returned wrong result, because the outer reference "t1.a"
in the subquery was substituted with the Item_ref item.
The Item_ref item obtains data from the result_field object
that refreshes once after the end of each group. This data
is not applicable to filesort since filesort() doesn't care
about groups (and doesn't update result_field objects with
copy_fields() and so on). Also that data is not applicable
to group separation algorithm: end_send_group() checks every
record with test_if_group_changed() that evaluates Item_ref
items, but it refreshes those Item_ref-s only after the end
of group, that is a vicious circle and the grouped column
values in the output are shifted.
Fix: if
a) we grouping by a subquery and
b) that subquery has outer references to FROM list
of the grouping query,
then we substitute these outer references with
Item_direct_ref like references under aggregate
functions: Item_direct_ref obtains data directly
from the current record.
2) The query with a non-trivial grouping expression like:
SELECT (SELECT t1.a) aa, COUNT(DISTINCT b) c
FROM t1 GROUP BY aa+0
also returned wrong result, since JOIN::exec() substitutes
references to top-level aliases in SELECT list with Item_copy
caching items. Item_copy items have same refreshing policy
as Item_ref items, so the whole groping expression with
Item_copy inside returns wrong result in filesort() and
end_send_group().
Fix: include aliased items into GROUP BY item tree instead
of Item_ref references to them.
logging is disabled
The server would hit an assertion because of a DBUG violation.
There was a missing DBUG_RETURN and instead a plain return
was used.
This patch replaces the return with DBUG_RETURN.
Performing fulltext prefix search (a word with truncation
operator) may cause a dead-loop. ft_min_word_len value
doesn't matter actually.
The problem was introduced along with "smarter index merge"
optimization.
There was two problems:
The first was the symptom, caused by bad error handling in
ha_partition. It did not handle print_error etc. when
having no partitions (when used by dummy handler).
The second was the real problem that when dropping tables
it reused the table type (storage engine) from when the lock
was asked for, not the table type that it had when gaining
the exclusive name lock. So that it tried to delete tables
from wrong storage engines.
Solutions for the first problem was to accept some handler
calls to the partitioning handler even if it was not setup
with any partitions, and also if possible fallback
to use the base handler's default functions.
Solution for the second problem was to remove the optimization
to reuse the definition from the cache, instead always check
the frm-file when holding the LOCK_open mutex
(updated with a fix for a debug print crash and better
comments as required by reviewer, and removed optimization
to avoid reading the frm-file).
Fixed 2 problems :
1. test_if_order_by_key() was continuing on the primary key
as if it has a primary key suffix (as the secondary keys do).
This leads to crashes in ORDER BY <pk>,<pk>.
Fixed by not treating the primary key as the secondary one
and not depending on it being clustered with a primary key.
2. The cost calculation was trying to read the records
per key when operating on ORDER BYs that order on all of the
secondary key + some of the primary key.
This leads to crashes because of out-of-bounds array access.
Fixed by assuming we'll find 1 record per key in such cases.
column is used for ORDER BY
Problem: filesort isn't meant for null length sort data
(e.g. char(0)), that leads to a server crash.
Fix: disregard sort order if sort data record length is 0 (nothing
to sort).
The problem was that a DROP TRIGGER statement inside a stored
procedure could cause a crash in subsequent invocations. This
was due to the addition, on the first execution, of a temporary
table reference to the stored procedure query table list. In
a subsequent invocation, there would be a attempt to reinitialize
the temporary table reference, which by then was already gone.
The solution is to backup and reset the query table list each
time a trigger needs to be dropped. This ensures that any temp
changes to the query table list are discarded. It is safe to
do so at this time as drop trigger is restricted from more
complicated scenarios (ie, not allowed within stored functions,
etc).
Server crashes when accessing ARCHIVE table with missing
.ARZ file.
When opening a table, ARCHIVE didn't properly pass through
error code from lower level azopen() to higher level open()
method.
Bulk REPLACE or bulk INSERT ... ON DUPLICATE KEY UPDATE may
break dynamic record MyISAM table.
The problem is limited to bulk REPLACE and INSERT ... ON
DUPLICATE KEY UPDATE, because only these operations may
be done via UPDATE internally and may request write cache.
When flushing write cache, MyISAM may write remaining
cached data at wrong position. Fixed by requesting write
cache to seek to a correct position.
table and view...
Invalid memory reads after a query referencing MyISAM table
multiple times with write lock. Invalid memory reads may
lead to server crash, valgrind warnings, incorrect values
in INFORMATION_SCHEMA.TABLES.{TABLE_ROWS, DATA_LENGTH,
INDEX_LENGTH, ...}.
This may happen when one of the table instances gets closed
after a query, e.g. out of slots in open tables cache. UNION,
MERGE and VIEW are irrelevant.
The problem was that MyISAM didn't restore state info
pointer to default value.
In case of 'CREATE VIEW' subselect transformation does not happen(see JOIN::prepare).
During fix_fields Item_row may call is_null() method for its arugmens which
leads to item calculation(wrong subselect in our case as
transformation did not happen before). This is_null() call
does not make sence for 'CREATE VIEW'.
Note:
Only Item_row is affected because other items don't call is_null()
during fix_fields() for arguments.
SHOW CREATE TABLE on a view (v1) that contains a function whose
statement uses another view (v2), could trigger a infinite loop
if the view referenced within the function causes a warning to
be raised while opening the said view (v2).
The problem was a infinite loop over the stack of internal error
handlers. The problem would be triggered if the stack contained
two or more handlers and the first two handlers didn't handle the
raised condition. In this case, the loop variable would always
point to the second handler in the stack.
The solution is to correct the loop variable assignment so that
the loop is able to iterate over all handlers in the stack.
The problem was that a failure to open a view wasn't being
properly handled. When opening a view with unknown definer,
the open procedure would be treated as successful and would
later crash when attempting to lock the view (which wasn't
opened to begin with).
The solution is to skip further processing when opening a
table if it fails with a fatal error.
error causes debug assertion
The IGNORE option of the multiple-table UPDATE command was
not intended to suppress errors caused by the
sql_safe_updates mode. This flag will raise an error if the
execution of UPDATE does not use a key for row retrieval,
and should continue do so regardless of the IGNORE option.
However the implementation of IGNORE does not support
exceptions to the rule; it always converts errors to
warnings and cannot be extended. The Internal_error_handler
interface offers the infrastructure to handle individual
errors, making sure that the error raised by
sql_safe_updates is not silenced.
Fixed by implementing an Internal_error_handler and using it
for UPDATE IGNORE commands.
Detailed revision comments:
r6489 | sunny | 2010-01-21 02:57:50 +0200 (Thu, 21 Jan 2010) | 2 lines
branches/5.1: Factor out test for bug#44030 from innodb-autoinc.test
into a separate test/result files.
Detailed revision comments:
r6488 | sunny | 2010-01-21 02:55:08 +0200 (Thu, 21 Jan 2010) | 2 lines
branches/5.1: Factor out test for bug#44030 from innodb-autoinc.test
into a separate test/result files.
check_access() returning false for a database does not
guarantee that the access is granted to it.
This wrong condition in filling the INFORMATION_SCHEMA
tables causes extra tables to be returned to the user
even if he has no rights to see them.
Fixed by correcting the condition.
fulltext search and row op.
The search for fulltext indexes is searching for some special
predicate layouts. While doing so it's not checking for the number
of columns of the expressions it tries to calculate.
And since row expressions can't return a single scalar value there
was a crash.
Fixed by checking if the expressions are scalar (in addition to
being constant) before calling Item::val_xxx() methods.
in multitable delete/subquery
SQL_BUFFER_RESULT should not have an effect on non-SELECT
statements according to our documentation.
Fixed by not passing it through to multi-table DELETE (similarly
to how it's done for multi-table UPDATE).
Several items said to be deprecated in the 4.1 manual
have never been removed. This worklog adds deprecation
warnings when these items are used, and warns the user
that the items will be removed in MySQL 5.6.
A couple of previously deprecation decision have been
reversed (see single file comments)
valgrind pointed to a buffer allocated by my_realloc which looked fishy
Replaced size with what was probably intended, added test case.
Now also fixed line after review comment
'CREATE TABLE IF NOT EXISTS ... SELECT' statement were causing 'CREATE
TEMPORARY TABLE ...' to be written to the binary log in row-based
mode (a.k.a. RBR), when there was a temporary table with the same name.
Because the 'CREATE TABLE ... SELECT' statement was executed as
'INSERT ... SELECT' into the temporary table. Since in RBR mode no
other statements related to temporary tables are written into binary log,
this sometimes broke replication.
This patch changes behavior of 'CREATE TABLE [IF NOT EXISTS] ... SELECT ...'.
it ignores existence of temporary table with the
same name as table being created and is interpreted
as attempt to create/insert into base table. This makes behavior of
'CREATE TABLE [IF NOT EXISTS] ... SELECT' consistent with
how ordinary 'CREATE TABLE' and 'CREATE TABLE ... LIKE' behave.
Selecting of the CONCAT_WS(...<PS parameter>...) result into
a user variable may return wrong data.
Item_func_concat_ws::val_str contains a number of memory
allocation-saving optimization tricks. After the fix
for bug 46815 the control flow has been changed to a
branch that is commented as "This is quite uncommon!":
one of places where we are trying to concatenate
strings inplace. However, that "uncommon" place
didn't care about PS parameters, that have another
trick in Item_sp_variable::val_str(): they use the
intermediate Item_sp_variable::str_value field,
where they may store a reference to an external
argument's buffer.
The Item_func_concat_ws::val_str function has been
modified to take into account val_str functions
(such as Item_sp_variable::val_str) that return a
pointer to an internal Item member variable that
may reference to a buffer provided.
MySQL handles the join syntax "JOIN ... USING( field1,
... )" and natural joins by building the same parse tree as
a corresponding join with an "ON t1.field1 = t2.field1 ..."
expression would produce. This parse tree was not cleaned up
properly in the following scenario. If a thread tries to
lock some tables and finds that the tables were dropped and
re-created while waiting for the lock, it cleans up column
references in the statement by means a per-statement free
list. But if the statement was part of a stored procedure,
column references on the stored procedure's free list weren't
cleaned up and thus contained pointers to freed objects.
Fixed by adding a call to clean up the current prepared
statement's free list.
In statement-based or mixed-mode replication, use DROP TEMPORARY TABLE
to drop multiple tables causes different errors on master and slave,
when one or more of these tables do not exist. Because when executed
on slave, it would automatically add IF EXISTS to the query to ignore
all ER_BAD_TABLE_ERROR errors.
To fix the problem, do not add IF EXISTS when executing DROP TEMPORARY
TABLE on the slave, and clear the ER_BAD_TABLE_ERROR error after
execution if the query does not expect any errors.
subselect_single_select_engine::exec()
When a subquery doesn't need to be evaluated because
it returns only aggregate functions and these aggregates
can be calculated from the metadata about the table it
was not updating all the relevant members of the JOIN
structure to reflect that this is a constant query.
This caused problems to the enclosing subquery
('<> SOME' in the test case above) trying to read some
data about the tables.
Fixed by setting const_tables to the number of tables
when the SELECT is optimized away.
