ContinuumIO/blaze — pull request #877 by mrocklin (2014-12-08 19:05:08+00:00)
Title: sql: count is robust to failing primary key

If The SQLAlchemy .primary_key attribute is missing its
.columns attribute starts returning []. This stateful change causes
problems in try-except code blocks as occurs in count on selections.

This change works around this issue in Blaze. We should probably
report up to SQLAlchemy as well.