SQLite does not store the rowid alias column in the record at all
when it is a rowid alias, because the rowid is always stored anyway
in the record header.
In case an ORDER BY column exactly matches a result column in the SELECT,
the insertion of the result column into the ORDER BY sorter can be skipped
because it's already necessarily inserted as a sorting column.
For this reason we have a mapping to know what index a given result column
has in the order by sorter.
This commit makes that mapping much simpler.
This change connects virtual tables with the query optimizer.
The optimizer now considers virtual tables during join order search
and invokes their best_index callbacks to determine feasible access
paths.
Currently, this is not a visible change, since none of the existing
extensions return information indicating that a plan is invalid.
Different scan parameters are required for different table types.
Currently, index and iteration direction are only used by B-tree tables,
while the remaining table types don’t require any parameters. Planning
access to virtual tables, however, will require passing additional
information from the planner, such as the virtual table index (distinct
from a B-tree index) and the constraints that must be forwarded to the
`filter` method.
The `best_index` implementation now returns a ResultCode along with the
IndexInfo. This allows it to signal specific outcomes, such as errors or
constraint violations. This change aligns better with SQLite’s xBestIndex
contract, where cases like missing constraints or invalid combinations of
constraints must not result in a valid plan.
Previously, there were two ways to indicate that a constraint should not
be passed to the filter function: setting `argv_index` to `None` or to
a value less than 1. This was redundant, so now only `None` is used.
Additional changes:
- Update IndexInfo documentation to clarify that constraint_usages must
have exact 1:1 correspondence with input ConstraintInfo array. The code
translating constraints into VFilter arguments heavily relies on this.
- Fix best_index implementation in test extension to comply with new
validation requirements by returning usage entry for each constraint
Support for attaching databases. The main difference from SQLite is that
we support an arbitrary number of attached databases, and we are not
bound to just 100ish.
We for now only support read-only databases. We open them as read-only,
but also, to keep things simple, we don't patch any of the insert
machinery to resolve foreign tables. So if an insert is tried on an
attached database, it will just fail with a "no such table" error - this
is perfect for now.
The code in core/translate/attach.rs is written by Claude, who also
played a key part in the boilerplate for stuff like the .databases
command and extending the pragma database_list, and also aided me in
the test cases.
There's no such thing as a read-only connection.
In a normal connection, you can have many attached databases. Some
r/o, some r/w.
To properly fix that, we also need to fix the OpenWrite opcode. Right
now we are passing a name, which is the name of the table. That
parameter is not used anywhere. That is also not what the SQLite opcode
specifies. Same as OpenRead, the p3 register should be the database
index.
With that change, we can - for now - pass the index 0, which is all
we support anyway, and then use that to test if we are r/o.
Two of the opcodes we implement (OpenRead and Transaction) should have
an opcode specifying the database to use, but they don't.
Add it, and for now always use 0 (the main database).
With this change, the following two queries are considered equivalent:
```sql
SELECT value FROM generate_series(5, 50);
SELECT value FROM generate_series WHERE start = 5 AND stop = 50;
```
Arguments passed in parentheses to the virtual table name are now
matched to hidden columns.
Column references are still not supported as table-valued function
arguments. The only difference is that previously, a query like:
```sql
SELECT one.value, series.value
FROM (SELECT 1 AS value) one, generate_series(one.value, 3) series;
```
would cause a panic. Now, it returns a proper error message instead.
Adding support for column references is more nuanced for two main
reasons:
- We need to ensure that in joins where a TVF depends on other tables,
those other tables are processed first. For example, in:
```sql
SELECT one.value, series.value
FROM generate_series(one.value, 3) series, (SELECT 1 AS value) one;
```
the one table must be processed by the top-level loop, and series must
be nested.
- For outer joins involving TVFs, the arguments must be treated as ON
predicates, not WHERE predicates.
We need to enumerate first and filter afterward — not the other way
around — because we later use the indexes produced by `enumerate` to
access the original `predicates` slice.
Fixes DELETE not emitting conditional jumps at all if the associated
WhereTerm is a constant, e.g.
```sql
limbo> create table t(x);
limbo> explain DELETE FROM t WHERE 5-5;
addr opcode p1 p2 p3 p4 p5 comment
---- ----------------- ---- ---- ---- ------------- -- -------
0 Init 0 7 0 0 Start at 7
1 OpenWrite 0 2 0 0 root=2; t
2 Rewind 0 6 0 0 Rewind table t
3 RowId 0 1 0 0 r[1]=t.rowid
4 Delete 0 0 0 0
5 Next 0 3 0 0
6 Halt 0 0 0 0
7 Transaction 0 1 0 0 write=true
8 Goto 0 1 0 0
```
I was adding more stuff to the simulator in a Branch of mine, and I
caught this error with delete. Upstreaming the fix here. As we do with
Update, I added the translation step for the `WhereTerms` of the query.
Edit: Closes#1732. Closes#1733. Closes#1734. Closes#1735. Closes
#1736. Closes#1738. Closes#1739. Closes#1740.
Edit: Also pushes constant where term translation to `init_loop` for
Update and Select as well.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#1746
Previously, the logic for collecting non-aggregate columns was duplicated
across multiple locations and implemented inconsistently. This caused a
bug that was revealed by the refactoring in this commit (see the added
test).
Again found when fuzzing nested where clause subqueries:
Aggregate registers need to be NULLed at the start because the same
registers might be reused on another invocation of a subquery, and if
they are not NULLed, the 2nd invocation of the same subquery will have
values left over from the first invocation.
Reviewed-by: Preston Thorpe (@PThorpe92)
Closes#1614
Currently we have this:
program.alloc_cursor_id(Option<String>, CursorType)`
where the String is the table's name or alias ('users' or 'u' in
the query).
This is problematic because this can happen:
`SELECT * FROM t WHERE EXISTS (SELECT * FROM t)`
There are two cursors, both with identifier 't'. This causes a bug
where the program will use the same cursor for both the main query
and the subquery, since they are keyed by 't'.
Instead introduce `CursorKey`, which is a combination of:
1. `TableInternalId`, and
2. index name (Option<String> -- in case of index cursors.
This should provide key uniqueness for cursors:
`SELECT * FROM t WHERE EXISTS (SELECT * FROM t)`
here the first 't' will have a different `TableInternalId` than the
second `t`, so there is no clash.
Currently in the main translation logic after planning and optimization,
we don't _really_ need to pass a &mut Vec<WhereTerm> around anymore, except
for the fact that virtual table constraint resolution is done ad-hoc in
`init_loop()`. Even there, the only thing we mutate is `WhereTerm::consumed`
which is a boolean indicating that the term has been "used up" by the optimizer
and shouldn't be evaluated as a normal where clause condition anymore.
In the upcoming branch for WHERE clause subqueries, I want to store immutable
references to WHERE clause expressions in `Resolver`, but this is unfortunately
not possible if we still use the aforementioned mutable references.
Hence, we can temporarily make `WhereTerm::consumed` a `Cell<bool>` which allows
us to pass an immutable reference to `init_loop()`, and the `Cell` can be removed
once the virtual table constraint resolution is moved to an earlier part of the
query processing pipeline.
