BUG#33946 - Join on Federated tables with Unique index gives error 1430

            from storage engine

Federated may crash a server, return wrong result set, return
"ERROR 1030 (HY000): Got error 1430 from storage engine" message
when local (engine=federated) table has a key against nullable
column.

The problem was wrong implementation of function that creates
WHERE clause for remote query from key.

mysql-test/r/federated.result

@@ -2045,6 +2045,30 @@ select 1 from t1 order by a;
 drop table t1;
 drop table t1;
 drop view v1;
+CREATE TABLE t1 (a INT, b INT, KEY(a,b));
+INSERT INTO t1 VALUES(NULL,1),(1,NULL),(NULL,NULL),(1,1),(2,2);
+CREATE TABLE t1 (a INT, b INT, KEY(a,b)) ENGINE=federated
+CONNECTION='mysql://root@127.0.0.1:SLAVE_PORT/test/t1';
+SELECT * FROM t1 WHERE a IS NULL;
+a	b
+NULL	NULL
+NULL	1
+SELECT * FROM t1 WHERE a IS NOT NULL;
+a	b
+1	NULL
+1	1
+2	2
+SELECT * FROM t1 WHERE a=1 AND b=1;
+a	b
+1	1
+SELECT * FROM t1 WHERE a IS NULL AND b=1;
+a	b
+NULL	1
+SELECT * FROM t1 WHERE a IS NOT NULL AND b=1;
+a	b
+1	1
+DROP TABLE t1;
+DROP TABLE t1;
 DROP TABLE IF EXISTS federated.t1;
 DROP DATABASE IF EXISTS federated;
 DROP TABLE IF EXISTS federated.t1;

mysql-test/t/federated.test

@@ -1716,5 +1716,26 @@ connection slave;
 drop table t1;
 drop view v1;
 
+#
+# BUG#33946 - Join on Federated tables with Unique index gives error 1430
+#             from storage engine
+#
+connection slave;
+CREATE TABLE t1 (a INT, b INT, KEY(a,b));
+INSERT INTO t1 VALUES(NULL,1),(1,NULL),(NULL,NULL),(1,1),(2,2);
+
+connection master;
+--replace_result $SLAVE_MYPORT SLAVE_PORT
+eval CREATE TABLE t1 (a INT, b INT, KEY(a,b)) ENGINE=federated
+CONNECTION='mysql://root@127.0.0.1:$SLAVE_MYPORT/test/t1';
+SELECT * FROM t1 WHERE a IS NULL;
+SELECT * FROM t1 WHERE a IS NOT NULL;
+SELECT * FROM t1 WHERE a=1 AND b=1;
+SELECT * FROM t1 WHERE a IS NULL AND b=1;
+SELECT * FROM t1 WHERE a IS NOT NULL AND b=1;
+DROP TABLE t1;
+
+connection slave;
+DROP TABLE t1;
 
 source include/federated_cleanup.inc;

sql/ha_federated.cc

@@ -1094,10 +1094,20 @@ bool ha_federated::create_where_from_key(String *to,
       {
         if (*ptr++)
         {
+          /*
+            We got "IS [NOT] NULL" condition against nullable column. We
+            distinguish between "IS NOT NULL" and "IS NULL" by flag. For
+            "IS NULL", flag is set to HA_READ_KEY_EXACT.
+          */
           if (emit_key_part_name(&tmp, key_part) ||
-              tmp.append(FEDERATED_ISNULL))
+              tmp.append(ranges[i]->flag == HA_READ_KEY_EXACT ?
+                         FEDERATED_ISNULL : " IS NOT NULL "))
             DBUG_RETURN(1);
-          continue;
+          /*
+            We need to adjust pointer and length to be prepared for next
+            key part. As well as check if this was last key part.
+          */
+          goto prepare_for_next_key_part;
         }
       }
 
@@ -1199,12 +1209,18 @@ bool ha_federated::create_where_from_key(String *to,
       if (tmp.append(FEDERATED_CLOSEPAREN))
         DBUG_RETURN(1);
 
+prepare_for_next_key_part:
       if (store_length >= length)
         break;
       DBUG_PRINT("info", ("remainder %d", remainder));
       DBUG_ASSERT(remainder > 1);
       length-= store_length;
-      ptr+= store_length;
+      /*
+        For nullable columns, null-byte is already skipped before, that is
+        ptr was incremented by 1. Since store_length still counts null-byte,
+        we need to subtract 1 from store_length.
+      */
+      ptr+= store_length - test(key_part->null_bit);
       if (tmp.append(FEDERATED_AND))
         DBUG_RETURN(1);