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

  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.


mysql-test/r/func_if.result:
  IF(x, unsigned, unsigned) should be unsigned.
mysql-test/r/view.result:
  Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.
mysql-test/t/func_if.test:
  IF(x, unsigned, unsigned) should be unsigned.
mysql-test/t/view.test:
  Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.
sql/item_cmpfunc.cc:
  Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.
  IF(x, unsigned, unsigned) should be unsigned.
sql/item_cmpfunc.h:
  Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.
sql/sql_yacc.yy:
  Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.

1 files changed, 86 insertions, 0 deletions

diff --git a/mysql-test/t/view.test b/mysql-test/t/view.test
index a5454b302f1..a418e25a576 100644
--- a/mysql-test/t/view.test
+++ b/mysql-test/t/view.test
@@ -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.