[PostgreSQL] New feature - Consider partial Index

[jullierme]

Please, consider partial Index (PostgreSQL)

A partial index is an index built over a subset of a table; the subset is defined by a conditional expression (called the predicate of the partial index). The index contains entries only for those table rows that satisfy the predicate.

SQL example

CREATE TABLE tests (
    subject text,
    target text,
    success boolean,
    ...
);

CREATE UNIQUE INDEX tests_success_constraint ON tests (subject, target)
    WHERE success is true;

Suggestion:

table test {
    subject text
    target text
    success boolean

    Indexes {
      (subject, target) [name: 'tests_success_constraint', unique, expression: `success is true`]
    }
}

Important note:

There is already a perfect comment from Yokozuna59 here issue 68 that could solve this one graciously