Makes it easier to test the feature:
```
$ cargo run -- --experimental-indexes
Limbo v0.0.22
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database
limbo> CREATE TABLE t(x);
limbo> CREATE INDEX t_idx ON t(x);
limbo> DROP INDEX t_idx;
```
Currently our "table id"/"table no"/"table idx" references always
use the direct index of the `TableReference` in the plan, e.g. in
`SelectPlan::table_references`. For example:
```rust
Expr::Column { table: 0, column: 3, .. }
```
refers to the 0'th table in the `table_references` list.
This is a fragile approach because it assumes the table_references
list is stable for the lifetime of the query processing. This has so
far been the case, but there exist certain query transformations,
e.g. subquery unnesting, that may fold new table references from
a subquery (which has its own table ref list) into the table reference
list of the parent.
If such a transformation is made, then potentially all of the Expr::Column
references to tables will become invalid. Consider this example:
```sql
-- Assume tables: users(id, age), orders(user_id, amount)
-- Get total amount spent per user on orders over $100
SELECT u.id, sub.total
FROM users u JOIN
(SELECT user_id, SUM(amount) as total
FROM orders o
WHERE o.amount > 100
GROUP BY o.user_id) sub
WHERE u.id = sub.user_id
-- Before subquery unnesting:
-- Main query table_references: [users, sub]
-- u.id refers to table 0, column 0
-- sub.total refers to table 1, column 1
--
-- Subquery table_references: [orders]
-- o.user_id refers to table 0, column 0
-- o.amount refers to table 0, column 1
--
-- After unnesting and folding subquery tables into main query,
-- the query might look like this:
SELECT u.id, SUM(o.amount) as total
FROM users u JOIN orders o ON u.id = o.user_id
WHERE o.amount > 100
GROUP BY u.id;
-- Main query table_references: [users, orders]
-- u.id refers to table index 0 (correct)
-- o.amount refers to table index 0 (incorrect, should be 1)
-- o.user_id refers to table index 0 (incorrect, should be 1)
```
We could ofc traverse every expression in the subquery and rewrite
the table indexes to be correct, but if we instead use stable identifiers
for each table reference, then all the column references will continue
to be correct.
Hence, this PR introduces a `TableInternalId` used in `TableReference`
as well as `Expr::Column` and `Expr::Rowid` so that this kind of query
transformations can happen with less pain.
we had an incorrect optimization in `eliminate_orderby_like_groupby()`
where it could remove e.g. the first term of the ORDER BY if it matched
the first GROUP BY term and the result set was naturally ordered by that
term. this is invalid. see e.g.:
```sql
main branch - BAD: removes the `ORDER BY id` term because the results are naturally ordered by id.
However, this results in sorting the entire thing by last name only!
limbo> select id, last_name, count(1) from users GROUP BY 1,2 order by id, last_name desc limit 3;
┌──────┬───────────┬───────────┐
│ id │ last_name │ count (1) │
├──────┼───────────┼───────────┤
│ 6235 │ Zuniga │ 1 │
├──────┼───────────┼───────────┤
│ 8043 │ Zuniga │ 1 │
├──────┼───────────┼───────────┤
│ 944 │ Zimmerman │ 1 │
└──────┴───────────┴───────────┘
after fix - GOOD:
limbo> select id, last_name, count(1) from users GROUP BY 1,2 order by id, last_name desc limit 3;
┌────┬───────────┬───────────┐
│ id │ last_name │ count (1) │
├────┼───────────┼───────────┤
│ 1 │ Foster │ 1 │
├────┼───────────┼───────────┤
│ 2 │ Salazar │ 1 │
├────┼───────────┼───────────┤
│ 3 │ Perry │ 1 │
└────┴───────────┴───────────┘
I also refactored sorters to always use the ast `SortOrder` instead of boolean vectors, and use the `compare_immutable()` utility we use inside btrees too.
Closes#1365
Previously columns that were indexed were updated only in the
BtreeTable, but not on Index table. This commit basically enables
updates on indexes too if they are needed.
