[branko_d]

Not so sure about aggregation, but what definitely takes forever is performance.

To make a non-trivial SQL query scale to non-trivial amounts of data, you have to understand the physical data organization and how query optimizer is likely to use it, which is kind of contradictory to the idea of the SQL as a "declarative" language where you just say what you want, and let the query optimizer figure out how to get it.

Instead, you have to design your indexes carefully to coax the optimizer into choosing a reasonable access path for your particular query. And do the same for all queries where performance is important.

Indexes are fundamentally not about data, but about access patterns. Which is what the developers are responsible for. That's why physical database design is a development task, not database administration task.

[fomine3]

I think RDB is one of the most leaky abstraction. Despite that, it's still very useful.