COUNT return nothing when no line match the criteria #8280
Description
OrientDB Version: 3.0.1, 3.0.0RC2
Java Version: 1.8.0_162
Java(TM) SE Runtime Environment (build 1.8.0_162-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.162-b12, mixed mode)
OS: MacOSX 10.13.4
Expected behavior
When counting elements of a class with a restriction
select count(*) from foo where name = 'bar'
I expect to get a single result with the count value event if no foo object has the name 'bar'.
In this case, the value of count should be 0.
Actual behavior
When the restriction is empty, count has no result at all.
Note, when there is no restriction but the class is empty, the query bahave has expected.
Note: the problem seams to come from a premature optimisation of the query plan that dump the result when the restriction is empty.
Steps to reproduce
Here is a scenario from the console 3.0.1. The same behavior happens in the java driver.
orientdb> create database memory:test
Creating database [memory:test] using the storage type [MEMORY]...
Database created successfully.
Current database is: memory:test
orientdb {db=test}> create class a
Class created successfully.
orientdb {db=test}> create property a.name string
Property created successfully.
orientdb {db=test}> select count(*) from a
+----+--------+
|# |count(*)|
+----+--------+
|0 |0 |
+----+--------+
1 item(s) found. Query executed in 0.004 sec(s).
orientdb {db=test}> insert into a (name) values ('a')
Inserted record '[a#25:0{name:a} v1]' in 0,009000 sec(s).
orientdb {db=test}> insert into a (name) values ('b')
Inserted record '[a#26:0{name:b} v1]' in 0,001000 sec(s).
orientdb {db=test}> insert into a (name) values ('c')
Inserted record '[a#27:0{name:c} v1]' in 0,001000 sec(s).
orientdb {db=test}> select count(*) from a
+----+--------+
|# |count(*)|
+----+--------+
|0 |3 |
+----+--------+
1 item(s) found. Query executed in 0.005 sec(s).
orientdb {db=test}> select count(*) from a where name = 'a'
+----+--------+
|# |count(*)|
+----+--------+
|0 |1 |
+----+--------+
1 item(s) found. Query executed in 0.013 sec(s).
orientdb {db=test}> select count(*) from a where name = 'd'
0 item(s) found. Query executed in 0.002 sec(s).
orientdb {db=test}>
The last command should return an item with 0.