I like that everyone is trying to make something like SQL that reads more naturally to them. More alternatives is good! SQL is a widely accepted standard, and has strictly defined and super broadly accepted semantics.
As someone who has written quite a few half-baked-for-general-use but fit-for-purpose SQL generator utilities over the years, I'll suggest that if you intend for a novel syntax to be a general SQL replacement then being isomorphic to SQL would massively increase usefulness and uptake:
1. novel syntax to SQL; check! Now novel syntax works with all the databases!
2. any valid SQL to novel syntax; a bit harder, but I'd start by using a SQL parser like https://github.com/pganalyze/libpg_query and translating the resulting AST into the novel syntax.
3. novel syntax to SQL back to novel syntax is idempotent; a nice side effect is a validator/formatter for "novel syntax"
4. SQL to novel syntax back to SQL is idempotent; a nice side effect is a validator/formatter for SQL, which would be awesome. (See also https://go.dev/blog/gofmt, which is where I learned this "round trip as formatter" trick.)
I don't mean for this to sound negative, and I know that 2, 3, and 4 are kind of hard. Thank you for building prql!
As someone who has written quite a few half-baked-for-general-use but fit-for-purpose SQL generator utilities over the years, I'll suggest that if you intend for a novel syntax to be a general SQL replacement then being isomorphic to SQL would massively increase usefulness and uptake:
1. novel syntax to SQL; check! Now novel syntax works with all the databases!
2. any valid SQL to novel syntax; a bit harder, but I'd start by using a SQL parser like https://github.com/pganalyze/libpg_query and translating the resulting AST into the novel syntax.
3. novel syntax to SQL back to novel syntax is idempotent; a nice side effect is a validator/formatter for "novel syntax"
4. SQL to novel syntax back to SQL is idempotent; a nice side effect is a validator/formatter for SQL, which would be awesome. (See also https://go.dev/blog/gofmt, which is where I learned this "round trip as formatter" trick.)
I don't mean for this to sound negative, and I know that 2, 3, and 4 are kind of hard. Thank you for building prql!