Fixed bug#18360: Incorrect type coercion in IN() results in false comparison

The IN() function uses agg_cmp_type() to aggregate all types of its arguments
to find out some common type for comparisons. In this particular case the 
char() and the int was aggregated to double because char() can contain values
like '1.5'. But all strings which do not start from a digit are converted to
0. thus 'a' and 'z' become equal. 
This behaviour is reasonable when all function arguments are constants. But 
when there is a field or an expression this can lead to false comparisons. In
this case it makes more sense to coerce constants to the type of the field
argument.

The agg_cmp_type() function now aggregates types of constant and non-constant
items separately. If some non-constant items will be found then their
aggregated type will be returned. Thus after the aggregation constants will be
coerced to the aggregated type. 


mysql-test/t/func_in.test:
  Added test case for bug#18360: Incorrect type coercion in IN() results in false comparison.
mysql-test/r/func_in.result:
  Added test case for bug#18360: Incorrect type coercion in IN() results in false comparison.
sql/item_cmpfunc.cc:
  Fixed bug#18360: Incorrect type coercion in IN() results in false comparison.
  The agg_cmp_type() function now aggregates types of constant and non-constant
  items separately. If some non-constant items will be found then their
  aggregated type will be returned. Thus after the aggregation constants will
  be coerced to the aggregated type.

1 files changed, 21 insertions, 0 deletions

diff --git a/mysql-test/r/func_in.result b/mysql-test/r/func_in.result
index 3cf2afc83d1..0632dddb87e 100644
--- a/mysql-test/r/func_in.result
+++ b/mysql-test/r/func_in.result
@@ -202,3 +202,24 @@ select count(*) from t1 where id not in (1,2);
 count(*)
 1
 drop table t1;
+create table t1 (f1 char(1), f2 int);
+insert into t1 values (1,0),('a',1),('z',2);
+select f1 from t1 where f1 in (1,'z');
+f1
+1
+z
+select f2 from t1 where f2 in (1,'z');
+f2
+0
+1
+select f1 from t1 where 'z' in (1,f1);
+f1
+z
+select * from t1 where 'z' in (f2,f1);
+f1	f2
+z	2
+select * from t1 where 1 in (f2,f1);
+f1	f2
+1	0
+a	1
+drop table t1;