Bug#28729: Field_enum wrongly reported an error while storing an empty string.

ENUM fields internally store their values as integers and may use integer
values as indexes to their values. Invalid values are mapped to zero value.
When storing an empty string the ENUM field fails to find an appropriate value
and tries to convert the provided string to integer. The conversion also
fails and error is returned even if the thd->count_cuted_fields is set to
CHECK_FIELD_IGNORE. This makes the range optimizer wrongly decide that an
impossible range is present.

Now the Field_enum::store() returns error while storing an empty string only
if the thd->count_cuted_fields isn't set to CHECK_FIELD_IGNORE.

mysql-test/r/type_enum.result

@@ -1779,3 +1779,10 @@ create table t1(exhausting_charset enum('ABCDEFGHIJKLMNOPQRSTUVWXYZ','

 
 !"','#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~','xx\','yy\','zz'));
 ERROR 42000: Field separator argument is not what is expected; check the manual
 End of 4.1 tests
+create table t1(f1 set('a','b'), index(f1));
+insert into t1 values(''),(''),('a'),('b');
+select * from t1 where f1='';
+f1
+
+
+drop table t1;

mysql-test/t/type_enum.test

@@ -157,3 +157,11 @@ create table t1(exhausting_charset enum('ABCDEFGHIJKLMNOPQRSTUVWXYZ','

 
 !"','#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~','xx\','yy\','zz'));
 
 --echo End of 4.1 tests
+
+#
+# Bug#28729: Field_enum wrongly reported an error while storing an empty string.
+#
+create table t1(f1 set('a','b'), index(f1));
+insert into t1 values(''),(''),('a'),('b');
+select * from t1 where f1='';
+drop table t1;

sql/field.cc

@@ -7643,6 +7643,8 @@ int Field_enum::store(const char *from,uint length,CHARSET_INFO *cs)
 	tmp=0;
 	set_warning(MYSQL_ERROR::WARN_LEVEL_WARN, WARN_DATA_TRUNCATED, 1);
       }
+      if (!table->in_use->count_cuted_fields)
+        err= 0;
     }
     else
       set_warning(MYSQL_ERROR::WARN_LEVEL_WARN, WARN_DATA_TRUNCATED, 1);