Add support for NULLS NOT DISTINCT clause

[rstular]

PostgreSQL 15 added support (section E.2.3.1.2. Indexes) for the NULLS NOT DISTINCT clause in index creation, which, as the name suggests, causes nulls to not be treated as distinct values when evaluating the UNIQUE constraint.

However, using this feature on an unsupported Postgres version will cause an SQL error - I'm not sure how/if this is handled in this project.

Also closes #509

[billy1624]

Hey @rstular, thanks for contributing!!

I think we miss a edge case (this should be added as test case):

assert_eq!(
    Table::create()
        .table(Glyph::Table)
        .col(ColumnDef::new(Glyph::Image).json())
        .col(ColumnDef::new(Glyph::Aspect).json_binary())
        .index(
            Index::create()
                .unique()
                .nulls_not_distinct()
                .name("idx-glyph-aspect-image")
                .table(Glyph::Table)
                .col(Glyph::Aspect)
                .col(Glyph::Image)
        )
        .to_string(PostgresQueryBuilder),
    [
        r#"CREATE TABLE "glyph" ("#,
        r#""image" json,"#,
        r#""aspect" jsonb,"#,
        r#"CONSTRAINT "idx-glyph-aspect-image" UNIQUE NULLS NOT DISTINCT ("aspect", "image")"#,
        r#")"#,
    ]
    .join(" ")
);

Hence, we need to modify this part as well:

sea-query/src/backend/postgres/index.rs

Lines 73 to 80 in c6becfa

	fn prepare_index_prefix(&self, create: &IndexCreateStatement, sql: &mut dyn SqlWriter) {
	if create.primary {
	write!(sql, "PRIMARY KEY ").unwrap();
	}
	if create.unique {
	write!(sql, "UNIQUE ").unwrap();
	}
	}

[billy1624]

Awesome!! Thanks! @rstular

[rstular]

@billy1624 Glad to help with the project :)

I've resolved the merge conflicts now, so this should (hopefully) be ready to merge.

[billy1624]

See you around on GitHub @rstular :)
Thanks again!