SQLite can create non-UNIQUE covering indexes, w/o any additional syntax,
but I thought there was also explicit syntax for that, but looking at [the doc] it
seems I was wrong.
Therefore, it appears to be impossible to create a **UNIQUE** covering index,
the way it's possible in [PostgreSQL] using the following syntax:
CREATE [UNIQUE] INDEX ... ON tab(cols...) INCLUDE(extra_cols...)
Any chance this can be added to SQLite? I suspect all the internal machinery
exists, with existing non-unique covering indexes, and without-rowid tables,
the only difference is that the uniqueness is enforced on a prefix of the
index's column(s) only.
This would bring parity between SQLite and PostgreSQL, always a good thing,
and allow to optimize queries to avoid index **and** table IO. Which is exactly
what I was trying to do, and discovered I couldn't in this case. My $0.02.
Here's my exact use case, FWIW:
CREATE TABLE enum (
cat int NOT NULL, -- category / kind
idx int NOT NULL, -- enum numeric ID
txt text NOT NULL, -- enum textual ID / name
[other columns...], -- additional "payload" columns
PRIMARY KEY (cat, idx)
) WITHOUT ROWID;
CREATE UNIQUE INDEX enum_by_txt ON enum(cat, txt) INCLUDE(idx);
I.e. equally fast *single-IO* access by (cat, idx) or (cat, txt).
The `enum` table and its index are mostly read-only, with writes
being append-only. Other tables will have FKs to (cat, idx), while
outside queries will join on those tables via the `enum.idx` table
but bind *textual IDs*, thus need `txt` to `idx` translation.