This is a very limited form of composition. It's very difficult to break a query down into a bunch of subcomponents that can be reused among groups of queries. CTEs are close, but it's really hard to achieve re-usability of a CTE unless you are stitching together strings at runtime.

Probably the closest you could get is a view, but even then if you have many views stitched together to form a query this can impact performance in ugly ways.

Generally in order to achieve the best performance and to get the most of out of the DB engine it seems like producing unique SQL for each query which is optimized for that query is generally the optimal approach.

In summary: Just because SQL is based on a few composable operations (map, filter), does not mean it is composable itself.