[fridental]

For the sake of God, please fucking stop inventing new pipe languages.

LINQ: exists

Splunk query language: exists

KQL: exists

MongoDB query language: exists

PRQL: exists

[pxc]

LINQ, Splunk, and KQL are all proprietary. For the purposes of setting new standards, they might as well not exist.

PRQL is the only real entrant in your list when it comes to adding a pipelining syntax to a language for relational queries in a way that others can freely build on.

[bvrmn]

SQL parsers: exists.

The paper clearly describes the goal: add a pipe syntax into existing systems with minor changes and be compatible with existing SQL queries.

BTW: LINQ is an AST transformer not a language per se tied to a particular platform. None of existing DBs allows to use it directly.