operations)
Before this change, the boolean predicates:
- X IS TRUE,
- X IS NOT TRUE,
- X IS FALSE,
- X IS NOT FALSE
were implemented by expanding the Item tree in the parser, by using a
construct like:
Item_func_if(Item_func_ifnull(X, <value>), <value>, <value>)
Each <value> was a constant integer, either 0 or 1.
A bug in the implementation of the function IF(a, b, c), in
Item_func_if::fix_length_and_dec(), would cause the following :
When the arguments b and c are both unsigned, the result type of the
function was signed, instead of unsigned.
When the result of the if function is signed, space for the sign could be
counted twice (in the max() expression for a signed argument, and in the
total), causing the member max_length to be too high.
An effect of this is that the final type of IF(x, int(1), int(1)) would be
int(2) instead of int(1).
With this fix, the problems found in Item_func_if::fix_length_and_dec()
have been fixed.
While it's semantically correct to represent 'X IS TRUE' with
Item_func_if(Item_func_ifnull(X, <value>), <value>, <value>),
there are however more problems with this construct.
a)
Building the parse tree involves :
- creating 5 Item instances (3 ints, 1 ifnull, 1 if),
- creating each Item calls my_pthread_getspecific_ptr() once in the operator
new(size), and a second time in the Item::Item() constructor, resulting
in a total of 10 calls to get the current thread.
Evaluating the expression involves evaluating up to 4 nodes at runtime.
This representation could be greatly simplified and improved.
b)
Transforming the parse tree internally with if(ifnull(...)) is fine as long
as this transformation is internal to the server implementation.
With views however, the result of the parse tree is later exposed by the
::print() functions, and stored as part of the view definition.
Doing this has long term consequences:
1)
The original semantic 'X IS TRUE' is lost, and replaced by the
if(ifnull(...)) expression. As a result, SHOW CREATE VIEW does not restore
the original code.
2)
Should a future version of MySQL implement the SQL BOOLEAN data type for
example, views created today using 'X IS NULL' can be exported using
mysqldump, and imported again. Such views would be converted correctly and
automatically to use a BOOLEAN column in the future version.
With 'X IS TRUE' and the current implementations, views using these
"boolean" predicates would not be converted during the export/import, and
would use integer columns instead.
The difference traces back to how SHOW CREATE VIEW preserves 'X IS NULL' but
does not preserve the 'X IS TRUE' semantic.
With this fix, internal representation of 'X IS TRUE' booleans predicates
has changed, so that:
- dedicated Item classes are created for each predicate,
- only 1 Item is created to represent 1 predicate
- my_pthread_getspecific_ptr() is invoked 1 time instead of 10
- SHOW CREATE VIEW preserves the original semantic, and prints 'X IS TRUE'.
Note that, because of the fix in Item_func_if, views created before this fix
will:
- correctly use a int(1) type instead of int(2) for boolean predicates,
- incorrectly print the if(ifnull(...), ...) expression in SHOW CREATE VIEW,
since the original semantic (X IS TRUE) has been lost.
- except for the syntax used in SHOW CREATE VIEW, these views will operate
properly, no action is needed.
Views created after this fix will operate correctly, and will preserve the
original code semantic in SHOW CREATE VIEW.
fails
The bug was introduced with the push of the fix for bug#20953: after
the error on view creation we never reset the error state, so some
valid statements would give the same error after that.
The solution is to properly reset the error state.
If SELECT-part of CREATE VIEW statement contains '\Z',
it is not handled correctly.
The problem was in String::print().
Symbol with code 032 (26) is replaced with '\z',
which is not supported by the lexer.
The fix is to replace the symbol with '\Z'.
Due to the complexity of this change, everything is documented in WL#3565
This patch is the third iteration, it takes into account the comments
received to date.
a updatable view.
When there's a VIEW on a base table that have AUTO_INCREMENT column, and
this VIEW doesn't provide an access such column, after INSERT to such
VIEW LAST_INSERT_ID() did not return the value just generated.
This behaviour is intended and correct, because if the VIEW doesn't list
some columns then these columns are effectively hidden from the user,
and so any side effects of inserting default values to them.
However, there was a bug that such statement inserting into a view would
reset LAST_INSERT_ID() instead of leaving it unchanged.
This patch restores the original value of LAST_INSERT_ID() instead of
resetting it to zero.
Problem: renaming of FRM file and ARC files didn't use file name
encoding, so RENAME TABLE for views failed for views having
"tricky" characters in their names.
Fix: adding build_table_filename() in missing places.
should fail to create
The problem was that this type of errors was checked during view
creation, which doesn't happen when CREATE VIEW is a statement of
a created stored routine.
The solution is to perform the checks at parse time. The idea of the
fix is that the parser checks if a construction just parsed is allowed
in current circumstances by testing certain flags, and this flags are
reset for VIEWs.
The side effect of this change is that if the user already have
such bogus routines, it will now get a error when trying to do
SHOW CREATE PROCEDURE proc;
(and some other) and when trying to execute such routine he will get
ERROR 1457 (HY000): Failed to load routine test.p5. The table mysql.proc is missing, corrupt, or contains bad data (internal code -6)
However there should be very few such users (if any), and they may
(and should) drop these bogus routines.
In a trigger or a function used in a statement it is possible to do
SELECT from a table being modified by the statement. However,
encapsulation of such SELECT into a view and selecting from a view
instead of direct SELECT was not possible.
This happened because tables used by views (which in their turn
were used from functions/triggers) were not excluded from checks
in unique_table() routine as it happens for the rest of tables
added to the statement table list for prelocking.
With this fix we ignore all such tables in unique_table(), thus
providing consistency: inside a trigger or a functions SELECT from
a view may be used where plain SELECT is allowed. Modification of
the same table from function or trigger is still disallowed. Also,
this patch doesn't affect the case where SELECT from the table being
modified is done outside of function of trigger, such SELECTs are
still disallowed (this limitation and visibility problem when function
select from a table being modified are subjects of bug 21326). See
also bug 22427.
