Improve ECP support for conditions like WHERE c1 = 1 AND lower(c3) = 'def'

[greenlion]

Conjuctions with functions should push down the constant evaluation portion, and push the remaining portion to the SQL layer for evaluation.

[greenlion]

Currently, creating an explicit index on c1 will allow the optimizer to use the index without ECP.

[greenlion]

Fixed in ecp_enhancement branch.

mysql> select count(*) from t2 where c2 = 'a' and upper(c2) = 'A';
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec)

mysql> explain analyze select count(*) from t2 where c2 = 'a' and upper(c2) = 'A';
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN                                                                                                                                                                                                                                                                            |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Aggregate: count(0)  (actual time=1.014..1.014 rows=1 loops=1)
    -> Filter: ((t2.c2 = 'a') and (upper(t2.c2) = 'A'))  (cost=0.46 rows=1) (actual time=0.979..1.009 rows=3 loops=1)
        -> Table scan on t2  (cost=0.46 rows=4) (actual time=0.969..0.996 rows=3 loops=1)
 |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

-- note disjunctions push to MySQL layer
mysql> explain analyze select count(*) from t2 where c2 = 'a' or upper(c2) = 'B';
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN                                                                                                                                                                                                                                                                           |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Aggregate: count(0)  (actual time=0.867..0.868 rows=1 loops=1)
    -> Filter: ((t2.c2 = 'a') or (upper(t2.c2) = 'B'))  (cost=0.46 rows=4) (actual time=0.845..0.862 rows=4 loops=1)
        -> Table scan on t2  (cost=0.46 rows=4) (actual time=0.839..0.849 rows=4 loops=1)
 |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)