Bug#35108 SELECT FROM REFERENTIAL_CONSTRAINTS crashes

referenced_key_name field can be uninitialized in the case when
referenced table is dropped.
Added codition which allows to handle this situation.

mysql-test/r/information_schema_inno.result

@@ -78,3 +78,14 @@ NULL	NULL
 db-1	t-2
 NULL	NULL
 drop database `db-1`;
+create table t1(id int primary key) engine = Innodb;
+create table t2(pid int, foreign key (pid) references t1(id)) engine = Innodb;
+set foreign_key_checks = 0;
+drop table t1;
+select UNIQUE_CONSTRAINT_NAME
+from information_schema.referential_constraints
+where constraint_schema = schema();
+UNIQUE_CONSTRAINT_NAME
+NULL
+drop table t2;
+set foreign_key_checks = 1;

mysql-test/t/information_schema_inno.test

@@ -76,3 +76,16 @@ select referenced_table_schema, referenced_table_name
 from information_schema.key_column_usage
 where constraint_schema = 'db-1';
 drop database `db-1`;
+
+#
+# Bug#35108 SELECT FROM REFERENTIAL_CONSTRAINTS crashes
+#
+create table t1(id int primary key) engine = Innodb;
+create table t2(pid int, foreign key (pid) references t1(id)) engine = Innodb;
+set foreign_key_checks = 0;
+drop table t1;
+select UNIQUE_CONSTRAINT_NAME
+from information_schema.referential_constraints
+where constraint_schema = schema();
+drop table t2;
+set foreign_key_checks = 1;

sql/sql_show.cc

@@ -5276,8 +5276,14 @@ get_referential_constraints_record(THD *thd, TABLE_LIST *tables,
                              f_key_info->referenced_db->length, cs);
       table->field[10]->store(f_key_info->referenced_table->str, 
                              f_key_info->referenced_table->length, cs);
+      if (f_key_info->referenced_key_name)
+      {
         table->field[5]->store(f_key_info->referenced_key_name->str, 
                                f_key_info->referenced_key_name->length, cs);
+        table->field[5]->set_notnull();
+      }
+      else
+        table->field[5]->set_null();
       table->field[6]->store(STRING_WITH_LEN("NONE"), cs);
       table->field[7]->store(f_key_info->update_method->str, 
                              f_key_info->update_method->length, cs);
@@ -6480,8 +6486,8 @@ ST_FIELD_INFO referential_constraints_fields_info[]=
    OPEN_FULL_TABLE},
   {"UNIQUE_CONSTRAINT_SCHEMA", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0,
    OPEN_FULL_TABLE},
-  {"UNIQUE_CONSTRAINT_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0,
-   OPEN_FULL_TABLE},
+  {"UNIQUE_CONSTRAINT_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0,
+   MY_I_S_MAYBE_NULL, 0, OPEN_FULL_TABLE},
   {"MATCH_OPTION", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, OPEN_FULL_TABLE},
   {"UPDATE_RULE", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, OPEN_FULL_TABLE},
   {"DELETE_RULE", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, OPEN_FULL_TABLE},