only const tables
The problem was caused by two shortcuts in the optimizer that
are inapplicable in the ROLLUP case.
Normally in a case when only const tables are involved in a
query, DISTINCT clause can be safely optimized away since there
may be only one row produced by the join. Similarly, we don't
need to create a temporary table to resolve DISTINCT/GROUP
BY/ORDER BY. Both of these are inapplicable when the WITH
ROLLUP modifier is present.
Fixed by disabling the said optimizations for the WITH ROLLUP
case.
with temporary tables
There were two problems the test case from this bug was
triggering:
1. JOIN::rollup_init() was supposed to wrap all constant Items
into another object for queries with the WITH ROLLUP modifier
to ensure they are never considered as constants and therefore
are written into temporary tables if the optimizer chooses to
employ them for DISTINCT/GROUP BY handling.
However, JOIN::rollup_init() was called before
make_join_statistics(), so Items corresponding to fields in
const tables could not be handled as intended, which was
causing all kinds of problems later in the query execution. In
particular, create_tmp_table() assumed all constant items
except "hidden" ones to be removed earlier by remove_const()
which led to improperly initialized Field objects for the
temporary table being created. This is what was causing crashes
and valgrind errors in storage engines.
2. Even when the above problem had been fixed, the query from
the test case produced incorrect results due to some
DISTINCT/GROUP BY optimizations being performed by the
optimizer that are inapplicable in the WITH ROLLUP case.
Fixed by disabling inapplicable DISTINCT/GROUP BY optimizations
when the WITH ROLLUP modifier is present, and splitting the
const-wrapping part of JOIN::rollup_init() into a separate
method which is now invoked after make_join_statistics() when
the const tables are already known.
Problem: setting Item_func_rollup_const::null_value property to argument's null_value
before (without) the argument evaluation may result in a crash due to wrong null_value.
Fix: use is_null() to set Item_func_rollup_const::null_value instead as it evaluates
the argument if necessary and returns a proper value.
The Item_func_rollup_const class is used for wrapping constants to avoid
wrong result for ROLLUP queries with DISTINCT and a constant in the select
list. This class is also used to wrap up a NULL constant but its null_value
wasn't set accordingly. This led to a server crash.
Now the null_value of an object of the Item_func_rollup_const class is set
by its fix_length_and_dec member function.
Integer values with 10 digits may or may not fit into an int column
(e.g. 2147483647 vs 6147483647).
Thus when creating a temp table column for such an int we must
use bigint instead.
Fixed to use bigint.
Also subsituted a "magic number" with a named constant.
some rollup rows (rows with NULLs for grouping attributes) if GROUP BY
list contained constant expressions.
This happened because the results of constant expressions were not put
in the temporary table used for duplicate elimination. In fact a constant
item from the GROUP BY list of a ROLLUP query can be replaced for an
Item_null_result object when a rollup row is produced .
Now the JOIN::rollup_init function wraps any constant item referenced in
the GROYP BY list of a ROLLUP query into an Item_func object of a special
class that is never detected as constant item. This ensures creation of
fields for such constant items in temporary tables and guarantees right
results when the result of the rollup operation first has to be written
into a temporary table, e.g. in the cases when duplicate elimination is
required.
Fix for bug 7894 replaces a field(s) in a non-aggregate function with a item
reference if such a field was specified in the GROUP BY clause in order to
get a correct result.
When ROLLUP is involved this lead to a wrong result due to value of a such
field is got through a copy function and copying happens after the function
evaluation.
Such replacement isn't needed if grouping is also done by such a function.
The change_group_ref() function now isn't called for a function present in
the group list.
Select_type in the EXPLAIN output for the query SELECT * FROM t1 was
'SIMPLE', while for the query SELECT * FROM v1, where the view v1
was defined as SELECT * FROM t1, the EXPLAIN output contained 'PRIMARY'
for the select_type column.
- Make the range-et-al optimizer produce E(#table records after table
condition is applied),
- Make the join optimizer use this value,
- Add "filtered" column to EXPLAIN EXTENDED to show
fraction of records left after table condition is applied
- Adjust test results, add comments
DESCRIBE returned the type BIGINT for a column of a view if the column
was specified by an expression over values of the type INT.
E.g. for the view defined as follows:
CREATE VIEW v1 SELECT COALESCE(f1,f2) FROM t1
DESCRIBE returned type BIGINT for the only column of the view if f1,f2 are
columns of the INT type.
At the same time DESCRIBE returned type INT for the only column of the table
defined by the statement:
CREATE TABLE t2 SELECT COALESCE(f1,f2) FROM t1.
This inconsistency was removed by the patch.
Now the code chooses between INT/BIGINT depending on the
precision of the aggregated column type.
Thus both DESCRIBE commands above returns type INT for v1 and t2.
For queries with GROUP BY and without hidden GROUP BY fields DISTINCT is
optimized away becuase such queries produce result set without duplicates.
But ROLLUP can add rows which may be same to some rows and this fact was
ignored.
Added check so if ROLLUP is present DISTINCT can't be optimized away.
Fixed bug #12885.
Forced inheritence of the maybe_null flag for the expressions
containing GROUP BY attributes in selects with ROLLUP.
olap.test, olap.result:
Added test case for bug #12885.
Added a test case for bug #11543.
sql_select.cc:
Fixed bug #11543.
A ROLLUP query could return a wrong result set when
its GROUP BY clause contained references to the same
column.
Fixed the results of a test for group_concat.
After the fix foor bug #11639 the results became
correct.
olap.result, olap.test:
Added a test case for bug #11639.
sql_select.cc:
Fixed bug #11639: a wrong result set when using a view
instead of the underlying table in a rollup query
executed through filesort.
The old code did not take into account that we always
use an Item_ref object when referring to a view column.
item.h:
Fixed bug #11639.
Now if two Item_ref items ref1 and ref2 refer to the same field
then ref1->eq(ref2) returns 1.
Ensure that 'null_value' is not accessed before val() is called in FIELD() functions
Fixed initialization of key maps. This fixes some problems with keys when you have more than 64 keys
Fixed that ROLLUP don't always create a temporary table. This fix ensures that func_gconcat.test results are now predictable
Fixed bug #10982.
item.cc:
Fixed bug #10982. In the function Item_ref::val_decimal
by mistake the method Item_ref::val_decimal was used
instead of Item_ref::val_decimal_result.
Added test cases for bug #7894.
sql_select.cc:
Fixed bug #7894: GROUP BY queries with ROLLUP returned
wrong results for expressions containing group by columns.
The fix ensured correct results by replacement of all
occurrences of group by fields in non-aggregate expressions
for corresponding ref objects and preventing creation of
fields in temporary tables for expression containing group
by fields.
Fixed bug #9681.
The bug happened with queries using derived tables specified by
a SELECT with ROLLUP, such as:
SELECT * FROM (SELECT a, SUM(a) FROM t1 GROUP BY a WITH ROLLUP) t2,
if column a of table t1 is declared as NOT NULL.
This was to the fact that the first column of the temporary table
created to contain the derived table erroneously inherited the NOT NULL
attribute from column a.
olap.result, olap.test:
Added a test case for bug #9681.
Added a test case for bug #8617.
sql_select.cc:
Fixed bug #8617.
Queries with ROLLUP and LIMIT n returned more than n rows
if SQL_CALC_FOUND_ROWS was used.
