Fix #encoding error by oracle_enhanced

[ojiry]

An error occurs because Oracle cannot omit FROM.

$ bin/rails c
Loading development environment (Rails 5.0.0.1)
ruby 2.3.3 [1] pry(main)> ::ActiveRecord::Base.connection.select_one("SELECT '' AS str;").values.first.encoding
   (2.4ms)  SELECT '' AS str;
ActiveRecord::StatementInvalid: OCIError: ORA-00911: invalid character: SELECT '' AS str;
from stmt.c:243:in oci8lib_230.bundle

In the case of Oracle, I want to execute the following SQL:

$ bin/rails c
Loading development environment (Rails 5.0.0.1)
ruby 2.3.3 [1] pry(main)> ::ActiveRecord::Base.connection.select_one("SELECT dummy FROM DUAL").values.first.encoding
   (0.9ms)  SELECT dummy FROM DUAL
=> #<Encoding:UTF-8>

ref. https://github.com/rsim/oracle-enhanced

[koic]

Hi @mshibuya, Thanks for maintenance.

I also want this patch. Is there information necessary for merging?

[mshibuya]

Merged in, thanks!

[koic]

Thanks for your merging 💚 💛 ❤️

[ojiry]

Thank you for merged :)