The problem is that we can not use make_cond_for_table().
This function relies on used_tables() condition
which is not set properly for subqueries.
As result subquery is not filtered out.
The fix is to use remove_eq_conds() function instead
of make_cond_for_table() func. 'remove_eq_conds()'
algorithm relies on const_item() value and it allows
to handle subqueries in right way.
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.
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.
IS NULL was not checking the correct row in a HAVING context.
At the first row of a new group (where the HAVING clause is evaluated)
the column and SELECT list references in the HAVING clause should
refer to the last row of the previous group and not to the current one.
This was not done for IS NULL, because it was using Item::is_null() doesn't
have a Item_is_null_result() counterpart to access the data from the
last row of the previous group. Note that all the Item::val_xxx() functions
(e.g. Item::val_int()) have their _result counterparts (e.g. Item::val_int_result()).
Fixed by implementing a is_null_result() (similarly to int_result()) and
calling this instead of is_null() column and SELECT list references inside
the HAVING clause.
This bug manifested itself for join queries with GROUP BY and HAVING clauses
whose SELECT lists contained DISTINCT. It occurred when the optimizer could
deduce that the result set would have not more than one row.
The bug could lead to wrong result sets for queries of this type because
HAVING conditions were erroneously ignored in some cases in the function
remove_duplicates.
- 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
The select statement that specified a view could be
slightly changed when the view was saved in a frm file.
In particular references to an alias name in the HAVING
clause could be substituted for the expression named by
this alias.
This could result in an error message for a query of
the form SELECT * FROM <view>. Yet no such message
appeared when executing the query specifying the view.
A query with a group by and having clauses could return a wrong
result set if the having condition contained a constant conjunct
evaluated to FALSE.
It happened because the pushdown condition for table with
grouping columns lost its constant conjuncts.
Pushdown conditions are always built by the function make_cond_for_table
that ignores constant conjuncts. This is apparently not correct when
constant false conjuncts are present.
The SQL standard doesn't allow to use in HAVING clause fields that are not
present in GROUP BY clause and not under any aggregate function in the HAVING
clause. However, mysql allows using such fields. This extension assume that
the non-grouping fields will have the same group-wise values. Otherwise, the
result will be unpredictable. This extension allowed in strict
MODE_ONLY_FULL_GROUP_BY sql mode results in misunderstanding of HAVING
capabilities.
The new error message ER_NON_GROUPING_FIELD_USED message is added. It says
"non-grouping field '%-.64s' is used in %-.64s clause". This message is
supposed to be used for reporting errors when some field is not found in the
GROUP BY clause but have to be present there. Use cases for this message are
this bug and when a field is present in a SELECT item list not under any
aggregate function and there is GROUP BY clause present which doesn't mention
that field. It renders the ER_WRONG_FIELD_WITH_GROUP error message obsolete as
being more descriptive.
The resolve_ref_in_select_and_group() function now reports the
ER_NON_GROUPING_FIELD_FOUND error if the strict mode is set and the field for
HAVING clause is found in the SELECT item list only.
The problem was due to the fact that with --lower-case-table-names set to 1
the function find_field_in_group did not convert the prefix 'HU' in
HU.PROJ.CITY into lower case when looking for it in the group list. Yet the
names in the group list were extended by the database name in lower case.
Multiple equalities were not adjusted after reading constant tables.
It resulted in neglecting good index based methods that could be
used to access of other tables.
A query with a group by and having clauses could return a wrong
result set if the having condition contained a constant conjunct
evaluated to FALSE.
It happened because the pushdown condition for table with
grouping columns lost its constant conjuncts.
Pushdown conditions are always built by the function make_cond_for_table
that ignores constant conjuncts. This is apparently not correct when
constant false conjuncts are present.
When the GROUP BY clause contains a column reference that can be resolved to
both an aliased column in the SELECT list, and to a column in the FROM clause,
the group column is resolved to the column in the FROM clause (for ANSI conformance).
However, it may be so that the user's intent is just the other way around, and he/she
gets the query results grouped by a completely different column than expexted.
This patch adds a warning in such cases that tells the user that there is potential
ambiguity in the group column.
sql/sql_select.cc
- Added a warning when a GROUP column is ambiguous due to that there is a
column reference with the same name both in the SELECT and FROM clauses.
In this case we resolve to the column in FROM clause and warn the user
of a possible ambiguity.
- More extensive comments.
- Changed the function to return bool instead of int (as in other places).
mysql-test/t/group_by.test
Added test for BUG#11211.
mysql-test/r/group_by.result
Added test for BUG#11211.
- Changed name resolution for GROUP BY so that derived columns do not shadow table columns
from the FROM clause. As a result GROUP BY now is handled as a true ANSI extentsion.
- Issue a warning when HAVING is resolved into ambiguous columns, and prefer the columns from
the GROUP BY clause over SELECT columns.
from the select list and TEXT field
make setup_copy_fields to insert Item_copy_string for blobs in
the beginning of the copy_funcs (push_back instead of push_front)
the thing is that Item_copy_string::copy for function can call
Item_copy_string::val_int for blob via Item_ref.
But if Item_copy_string::copy for blob isn't called before,
it's value will be wrong.
So all the Item_copy_string::copy for blobs should be called before
Item_copy_string::copy for functions.
