Handle joins on the same table by using sqlalchemy alias
forgot the import on alias stuff
join: repeated columns handled with relabel
expr: join on same table test
Merge branch 'master' of https://github.com/luccasmenezes/blaze into join-same-columns
join: handle overlapping fields with new schema, not a relabel
sql: Join on same table

Support aliasing when the table name is the same

Pick out columns in a more explicit way to how expr does it
remove unneccessary alias import
sql: index based on position, not name

Joins now have different names than their sql counterparts
We index based on position rather than field name
sql: increase coverage by adding tests
sql: increase coverage by removing dead code
Merge pull request #811 from mrocklin/join-same-columns

Join same columns
Add length expression
Add NRows expression
Implement NRows for different backends
Clean up star imports
Move to reductions
Rename NRows -> nrows
Use None instead of {}
Import cleanup