rails/rails — comment on commit 6a28c512e358a95bbabd24af9d2b0608df787158
File:  line 0
By yahonda:

It fails if PosgreSQL version < 9.0.

```sql
ActiveRecord::StatementInvalid: PGError: ERROR: syntax error at or near "exists"
LINE 1: alter table developers drop column if exists zomg
```