Select of a hardcoded value returns Option<T> instead of just T about sqlx

[abonander]

This is a known issue because of how null inference works in the Postgres driver. Null inference takes its seed data from NOT NULL flags on table columns, so any output that doesn't come from a table can't be null-checked.

This is explained in the documentation: https://docs.rs/sqlx/latest/sqlx/macro.query.html#nullability-output-columns

Fixing this would require parsing the query, which is kind of a non-starter. There are crates that exist for this, but I'm not particularly impressed with them. The performance of the query macros depends highly on the amount of code that runs in them since they compile in debug mode by default, so the less we run the better.

The EXPLAIN output does include the expression for each column, so we could limit ourselves to just parsing the expression itself. That's something we could potentially do in-tree.