Bug #12876932 - INCORRECT SELECT RESULT ON FEDERATED TABLE

Problem description:
Table 't' created with two colums having compound index on both the 
columns under innodb/myisam engine at remote machine. In the local 
machine same table is created undet the federated engine.
A select having where clause with along 'AND' operation gives wrong 
results on local machine.

Analysis: 
The given query at federated engine is wrongly transformed by 
federated::create_where_from_key() function and the same was sent to 
the remote machine. Hence the local machine is showing wrong results.

Given query "select c1 from t where c1 <= 2 and c2 = 1;"
Query transformed, after ha_federated::create_where_from_key() function is:
SELECT `c1`, `c2` FROM `t` WHERE  (`c1` IS NOT NULL ) AND 
( (`c1` >= 2)  AND  (`c2` <= 1) ) and the same sent to real_query().
In the above the '<=' and '=' conditions were transformed to '>=' and 
'<=' respectively.

ha_federated::create_where_from_key() function behaving as below:
The key_range is having both the start_key and end_key. The start_key 
is used to get "(`c1` IS NOT NULL )" part of the where clause, this 
transformation is correct. The end_key is used to get "( (`c1` >= 2) 
AND  (`c2` <= 1) )", which is wrong, here the given conditions('<=' and '=') 
are changed as wrong conditions('>=' and '<=').
The end_key is having {key = 0x39fa6d0 "", length = 10, keypart_map = 3, 
flag = HA_READ_AFTER_KEY}

The store_length is having value '5'. Based on store_length and length 
values the condition values is applied in HA_READ_AFTER_KEY switch case.
The switch case 'HA_READ_AFTER_KEY' is applicable to only the last part of 
the end_key and for previous parts it is going to 'HA_READ_KEY_OR_NEXT' case, 
here the '>=' is getting added as a condition instead of '<='.

Fix:
Updated the 'if' condition in 'HA_READ_AFTER_KEY' case to affect for all 
parts of the end_key. i.e 'i > 0' will used for end_key, Hence added it in 
the if condition.

1 files changed, 1 insertions, 1 deletions

diff --git a/storage/federated/ha_federated.cc b/storage/federated/ha_federated.cc
index ae65aeb4cbb..7dd4f6b7149 100644
--- a/storage/federated/ha_federated.cc
+++ b/storage/federated/ha_federated.cc
@@ -1364,7 +1364,7 @@ bool ha_federated::create_where_from_key(String *to,
           break;
         }
         DBUG_PRINT("info", ("federated HA_READ_AFTER_KEY %d", i));
-        if (store_length >= length) /* end key */
+        if ((store_length >= length) || (i > 0)) /* for all parts of end key*/
         {
           if (emit_key_part_name(&tmp, key_part))
             goto err;