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Last tested: Nov 7, 2017
This error sometimes shows up in the logs when a migration is halted before it completes and Looker starts the migration over again upon net startup:
[ERROR | <threadid> | main] :: Error starting Looker: Java::JavaSql::SQLSyntaxErrorException: Table '<tablename>'/ Column '<column_name>' already exists
You need to restore from a backup when this happens.