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Bug#24532 (The return data type of IS TRUE is different from similar

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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.
This commit is contained in:
malff/marcsql@weblab.(none)
2007-02-12 13:59:29 -07:00
parent b5f8b6363d
commit 4e556b2305
7 changed files with 391 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
mysql-test/r/func_if.result
View File

@ -128,3 +128,6 @@ f1 f2 if(f1, 40.0, 5.00)
0 0 5.00
1 1 40.00
drop table t1;
select if(0, 18446744073709551610, 18446744073709551610);
if(0, 18446744073709551610, 18446744073709551610)
18446744073709551610

125
mysql-test/r/view.result
View File

@ -3033,4 +3033,129 @@ ERROR HY000: View's SELECT contains a subquery in the FROM clause
SELECT * FROM (SELECT 1) AS t;
1
1
drop view if exists view_24532_a;
drop view if exists view_24532_b;
drop table if exists table_24532;
create table table_24532 (
a int,
b bigint,
c int(4),
d bigint(48)
);
create view view_24532_a as
select
a IS TRUE,
a IS NOT TRUE,
a IS FALSE,
a IS NOT FALSE,
a IS UNKNOWN,
a IS NOT UNKNOWN,
a is NULL,
a IS NOT NULL,
ISNULL(a),
b IS TRUE,
b IS NOT TRUE,
b IS FALSE,
b IS NOT FALSE,
b IS UNKNOWN,
b IS NOT UNKNOWN,
b is NULL,
b IS NOT NULL,
ISNULL(b),
c IS TRUE,
c IS NOT TRUE,
c IS FALSE,
c IS NOT FALSE,
c IS UNKNOWN,
c IS NOT UNKNOWN,
c is NULL,
c IS NOT NULL,
ISNULL(c),
d IS TRUE,
d IS NOT TRUE,
d IS FALSE,
d IS NOT FALSE,
d IS UNKNOWN,
d IS NOT UNKNOWN,
d is NULL,
d IS NOT NULL,
ISNULL(d)
from table_24532;
describe view_24532_a;
Field Type Null Key Default Extra
a IS TRUE int(1) NO 0
a IS NOT TRUE int(1) NO 0
a IS FALSE int(1) NO 0
a IS NOT FALSE int(1) NO 0
a IS UNKNOWN int(1) NO 0
a IS NOT UNKNOWN int(1) NO 0
a is NULL int(1) NO 0
a IS NOT NULL int(1) NO 0
ISNULL(a) int(1) NO 0
b IS TRUE int(1) NO 0
b IS NOT TRUE int(1) NO 0
b IS FALSE int(1) NO 0
b IS NOT FALSE int(1) NO 0
b IS UNKNOWN int(1) NO 0
b IS NOT UNKNOWN int(1) NO 0
b is NULL int(1) NO 0
b IS NOT NULL int(1) NO 0
ISNULL(b) int(1) NO 0
c IS TRUE int(1) NO 0
c IS NOT TRUE int(1) NO 0
c IS FALSE int(1) NO 0
c IS NOT FALSE int(1) NO 0
c IS UNKNOWN int(1) NO 0
c IS NOT UNKNOWN int(1) NO 0
c is NULL int(1) NO 0
c IS NOT NULL int(1) NO 0
ISNULL(c) int(1) NO 0
d IS TRUE int(1) NO 0
d IS NOT TRUE int(1) NO 0
d IS FALSE int(1) NO 0
d IS NOT FALSE int(1) NO 0
d IS UNKNOWN int(1) NO 0
d IS NOT UNKNOWN int(1) NO 0
d is NULL int(1) NO 0
d IS NOT NULL int(1) NO 0
ISNULL(d) int(1) NO 0
create view view_24532_b as
select
a IS TRUE,
if(ifnull(a, 0), 1, 0) as old_istrue,
a IS NOT TRUE,
if(ifnull(a, 0), 0, 1) as old_isnottrue,
a IS FALSE,
if(ifnull(a, 1), 0, 1) as old_isfalse,
a IS NOT FALSE,
if(ifnull(a, 1), 1, 0) as old_isnotfalse
from table_24532;
describe view_24532_b;
Field Type Null Key Default Extra
a IS TRUE int(1) NO 0
old_istrue int(1) NO 0
a IS NOT TRUE int(1) NO 0
old_isnottrue int(1) NO 0
a IS FALSE int(1) NO 0
old_isfalse int(1) NO 0
a IS NOT FALSE int(1) NO 0
old_isnotfalse int(1) NO 0
show create view view_24532_b;
View Create View
view_24532_b CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `view_24532_b` AS select (`table_24532`.`a` is true) AS `a IS TRUE`,if(ifnull(`table_24532`.`a`,0),1,0) AS `old_istrue`,(`table_24532`.`a` is not true) AS `a IS NOT TRUE`,if(ifnull(`table_24532`.`a`,0),0,1) AS `old_isnottrue`,(`table_24532`.`a` is false) AS `a IS FALSE`,if(ifnull(`table_24532`.`a`,1),0,1) AS `old_isfalse`,(`table_24532`.`a` is not false) AS `a IS NOT FALSE`,if(ifnull(`table_24532`.`a`,1),1,0) AS `old_isnotfalse` from `table_24532`
insert into table_24532 values (0, 0, 0, 0);
select * from view_24532_b;
a IS TRUE old_istrue a IS NOT TRUE old_isnottrue a IS FALSE old_isfalse a IS NOT FALSE old_isnotfalse
0 0 1 1 1 1 0 0
update table_24532 set a=1;
select * from view_24532_b;
a IS TRUE old_istrue a IS NOT TRUE old_isnottrue a IS FALSE old_isfalse a IS NOT FALSE old_isnotfalse
1 1 0 0 0 0 1 1
update table_24532 set a=NULL;
select * from view_24532_b;
a IS TRUE old_istrue a IS NOT TRUE old_isnottrue a IS FALSE old_isfalse a IS NOT FALSE old_isnotfalse
0 0 1 1 0 0 1 1
drop view view_24532_a;
drop view view_24532_b;
drop table table_24532;
End of 5.0 tests.

11
mysql-test/t/func_if.test
View File

@ -97,3 +97,14 @@ create table t1 (f1 int, f2 int);
insert into t1 values(1,1),(0,0);
select f1, f2, if(f1, 40.0, 5.00) from t1 group by f1 order by f2;
drop table t1;
#
# Bug#24532 (The return data type of IS TRUE is different from similar
# operations)
#
# IF(x, unsigned, unsigned) should be unsigned.
#
select if(0, 18446744073709551610, 18446744073709551610);

86
mysql-test/t/view.test
View File

@ -2992,5 +2992,91 @@ eval CREATE VIEW v1 AS $query;
--echo # Previously the following would fail.
eval $query;
#
# Bug#24532: The return data type of IS TRUE is different from similar
# operations
#
--disable_warnings
drop view if exists view_24532_a;
drop view if exists view_24532_b;
drop table if exists table_24532;
--enable_warnings
create table table_24532 (
a int,
b bigint,
c int(4),
d bigint(48)
);
create view view_24532_a as
select
a IS TRUE,
a IS NOT TRUE,
a IS FALSE,
a IS NOT FALSE,
a IS UNKNOWN,
a IS NOT UNKNOWN,
a is NULL,
a IS NOT NULL,
ISNULL(a),
b IS TRUE,
b IS NOT TRUE,
b IS FALSE,
b IS NOT FALSE,
b IS UNKNOWN,
b IS NOT UNKNOWN,
b is NULL,
b IS NOT NULL,
ISNULL(b),
c IS TRUE,
c IS NOT TRUE,
c IS FALSE,
c IS NOT FALSE,
c IS UNKNOWN,
c IS NOT UNKNOWN,
c is NULL,
c IS NOT NULL,
ISNULL(c),
d IS TRUE,
d IS NOT TRUE,
d IS FALSE,
d IS NOT FALSE,
d IS UNKNOWN,
d IS NOT UNKNOWN,
d is NULL,
d IS NOT NULL,
ISNULL(d)
from table_24532;
describe view_24532_a;
create view view_24532_b as
select
a IS TRUE,
if(ifnull(a, 0), 1, 0) as old_istrue,
a IS NOT TRUE,
if(ifnull(a, 0), 0, 1) as old_isnottrue,
a IS FALSE,
if(ifnull(a, 1), 0, 1) as old_isfalse,
a IS NOT FALSE,
if(ifnull(a, 1), 1, 0) as old_isnotfalse
from table_24532;
describe view_24532_b;
show create view view_24532_b;
insert into table_24532 values (0, 0, 0, 0);
select * from view_24532_b;
update table_24532 set a=1;
select * from view_24532_b;
update table_24532 set a=NULL;
select * from view_24532_b;
drop view view_24532_a;
drop view view_24532_b;
drop table table_24532;
--echo End of 5.0 tests.