You're reading something into my comment I didn't want to say too
I just felt the need to point out that declarative languages are essentially always a DSL, wherever this DSL is actually performant and should be used depends on it's implementation.
Generally speaking, SQL is very well implemented so using any of the well established databases is probably a good choice. Nonetheless, few declarative languages come even close to SQLs efficient implementation so they're very rarely the answer.
I just felt the need to point out that declarative languages are essentially always a DSL, wherever this DSL is actually performant and should be used depends on it's implementation.
Generally speaking, SQL is very well implemented so using any of the well established databases is probably a good choice. Nonetheless, few declarative languages come even close to SQLs efficient implementation so they're very rarely the answer.