At the end of execution top level join execution
we cleanup this join with true argument.
It leads to underlying join cleanup(subquery) with true argument too
and to tmp_table_param->field array cleanup which is required later.
The problem is that Item_func_set_user_var does not set
result_filed which leads to unnecessary repeated excution of subquery
on final stage.
The fix is to set result_field for Item_func_set_user_var.
Problem: storing "SELECT ... INTO @var ..." results in variables we used val_xxx()
methods which returned results of the current row.
So, in some cases (e.g. SELECT DISTINCT, GROUP BY or HAVING) we got data
from the first row of a new group (where we evaluate a clause) instead of
data from the last row of the previous group.
Fix: use val_xxx_result() counterparts to get proper results.
in trigger
Interchangeable calls to the mysql_change_user client function
and invocations of a trigger changing some user variable caused
a memory corruption and a crash.
The mysql_change_user API call forces TDH::cleanup() on a server
that frees user variable entries.
However it didn't reset Item_func_set_user_var::entry to NULL
because Item_func_set_user_var::cleanup() was not overloaded.
So, Item_func_set_user_var::entry held a pointer to freed memory,
that caused a crash.
The Item_func_set_user_var::cleanup method has been overloaded
to cleanup the Item_func_set_user_var::entry field.
columns data types
The "SELECT @lastId, @lastId := Id FROM t" query returns
different result sets depending on the type of the Id column
(INT or BIGINT).
Note: this fix doesn't cover the case when a select query
references an user variable and stored function that
updates a value of that variable, in this case a result
is indeterminate.
The server uses incorrect assumption about a constantness of
an user variable value as a select list item:
The server caches a last query number where that variable
was changed and compares this number with a current query
number. If these numbers are different, the server guesses,
that the variable is not updating in the current query, so
a respective select list item is a constant. However, in some
common cases the server updates cached query number too late.
The server has been modified to memorize user variable
assignments during the parse phase to take them into account
on the next (query preparation) phase independently of the
order of user variable references/assignments in a select
item list.
The Item_func_set_user_var::register_field_in_read_map() did not check
that the result_field was null.This caused server crashes for queries that
required order by such a field and were executed without using a temporary
table.
The Item_func_set_user_var::register_field_in_read_map() now checks the
result_field to be not null.
Problem: there's no guarantee that the user variable item's result_field
is assigned when we're adjusting its table read map.
Fix: check the result_field before using it.
This is an additional fix.
Item::val_xxx methods are supposed to use original data source and
Item::val_xxx_result methods to use the item's result field. But for the
Item_func_set_user_var class val_xxx_result methods were mapped to val_xxx
methods. This leads, in particular, to producing bad sort keys and thus
wrong order of the result set of queries with group by/order by clauses.
The set of val_xxx_result methods is added to the Item_func_set_user_var
class. It's the same as the val_xxx set of method but uses the result_field
to return a value.
The end_update() function uses the Item::save_org_in_field() function to
save original values of items into the group buffer. But for the
Item_func_set_user_var this method was mapped to the save_in_field method.
The latter function wrongly decides to use the result_field. This leads to
saving incorrect value in the grouping buffer and wrong result of the whole
query.
The can_use_result_field argument of the bool type is added to the
Item_func_set_user_var::save_in_field() function. If it is set to FALSE
then the item's result field won't be used. Otherwise it will be detected
whether the result field will be used (old behaviour).
Two wrapping functions for the function above are added to the
Item_func_set_user_var class:
the save_in_field(Field *field, bool no_conversions) - it calls the above
function with the can_use_result_field set to TRUE.
the save_org_in_field(Field *field) - same, but the can_use_result_field
is set to FALSE.
- Adding variable m_cached_result_type to keep the variable type consistent
during the execution of a statement.
- Before each result set is returned to the client the description of each
column is sent as meta data.
Previously the result type for a column could change if the hash variable
entry changed between statements. This caused the result set of the query
to alternate column types in certain cases which is not supported by MySQL
client-server protocol. Example:
Previously this sequence:
SET @a:=1;
SELECT @a:="text", @a;
would return "text", "text";
After the change the SELECT returns "text", 0
The reson for this is that previously the result set from 'SELECT @a;'
would always be of the type STRING, whereas now the type of the variable
is taken from the last SET statement. However, 'SELECT @a:="text"' will
return type of STRING since the right side of the assignment is used.
used.
The Item::save_in_field() function is called from fill_record() to fill the
new row with data while execution of the CREATE TABLE ... SELECT statement.
Item::save_in_field() calls val_xxx() methods in order to get values.
val_xxx() methods do not take into account the result field. Due to this
Item_func_set_user_var::val_xxx() methods returns values from the original
table, not from the temporary one.
The save_in_field() member function is added to the Item_func_set_user_var
class. It detects whether the result field should be used and properly updates
the value of the user variable.
used.
Sorting by RAND() uses a temporary table in order to get a correct results.
User defined variable was set during filling the temporary table and later
on it is substituted for its value from the temporary table. Due to this
it contains the last value stored in the temporary table.
Now if the result_field is set for the Item_func_set_user_var object it
updates variable from the result_field value when being sent to a client.
The Item_func_set_user_var::check() now accepts a use_result_field
parameter. Depending on its value the result_field or the args[0] is used
to get current value.
Gluh's SESSION/GLOBAL for @variables fix in sql_yacc.yy and
Bar's well_formed_len() changes in ndb code
did not make it and should be re-applied manually
Now one can use user variables as target for data loaded from file
(besides table's columns). Also LOAD DATA got new SET-clause in which
one can specify values for table columns as expressions.
For example the following is possible:
LOAD DATA INFILE 'words.dat' INTO TABLE t1 (a, @b) SET c = @b + 1;
This patch also implements new way of replicating LOAD DATA.
Now we do it similarly to other queries.
We store LOAD DATA query in new Execute_load_query event
(which is last in the sequence of events representing LOAD DATA).
When we are executing this event we simply rewrite part of query which
holds name of file (we use name of temporary file) and then execute it
as usual query. In the beggining of this sequence we use Begin_load_query
event which is almost identical to Append_file event
independently from the expression it is initialized from.
In other words, this change treats a user variable like
a table with one column and one record. Discussed with
PeterG, Serg and Lars. This change also simplifies replication
allowing not to replicate variables' coercibility.
