closes#1185
## The Problem:
The underlying schema of virtual tables is hidden from the query
planner, and it currently has no way of optimizing select queries with
vtab table refs by using indexes or removing non-constant predicates.
All vtabs are currently rewound completely each time and any conditional
filtering is done in the vdbe layer instead of in the `VFilter`.
## The solution:
Add xBestIndex to the vtab module API to let extensions return some
`IndexInfo` that will allow the query planner to make better
optimizations and possibly omit conditionals
## Examples:
table `t`: vtab: (key, value)
table `t2`: table: (a,b)
### Join where vtab is outer table:
Properly pushes predicate to VFilter, which receives the idx_str
`key_eq` arg, telling it that there is a useable where clause on the key
"index"
### Join where vtab is inner table:
Constraint is not sent because it is marked as unusable
### Where clause on "indexed" column:
Pushed down and the predicate is omitted from the VDBE layer.
### Where clause on regular column:
No idx info received from BestIndex, VDBE handles conditional.
## TODO:
OrderBy info needs to be sent to xBestIndex and its not in a great
position in `open_loop` currently
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#1264
### Feat:
- Adds support for descending indexes
### Testing:
- Augments existing compound key index seek fuzz test to test for
various combinations of ascending and descending indexed columns. To
illustrate, the test runs 10000 queries like this on 8 different tables
with all different asc/desc permutations of a three-column primary key
index:
```sql
query: SELECT * FROM t WHERE x = 2826 LIMIT 5
query: SELECT * FROM t WHERE x = 671 AND y >= 2447 ORDER BY x ASC, y DESC LIMIT 5
query: SELECT * FROM t WHERE x = 2412 AND y = 589 AND z >= 894 ORDER BY x DESC LIMIT 5
query: SELECT * FROM t WHERE x = 1217 AND y = 1437 AND z <= 265 ORDER BY x ASC, y ASC, z DESC LIMIT 5
query: SELECT * FROM t WHERE x < 138 ORDER BY x DESC LIMIT 5
query: SELECT * FROM t WHERE x = 1312 AND y = 2757 AND z > 39 ORDER BY x DESC, y ASC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x = 1829 AND y >= 1629 ORDER BY x ASC, y ASC LIMIT 5
query: SELECT * FROM t WHERE x = 2047 ORDER BY x DESC LIMIT 5
query: SELECT * FROM t WHERE x = 893 AND y > 432 ORDER BY y DESC LIMIT 5
query: SELECT * FROM t WHERE x = 1865 AND y = 784 AND z <= 785 ORDER BY x DESC, y DESC, z DESC LIMIT 5
query: SELECT * FROM t WHERE x = 213 AND y = 1475 AND z <= 2870 ORDER BY x ASC, y ASC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x >= 1780 ORDER BY x ASC LIMIT 5
query: SELECT * FROM t WHERE x = 1983 AND y = 602 AND z = 485 ORDER BY y ASC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x = 2311 AND y >= 31 ORDER BY y DESC LIMIT 5
query: SELECT * FROM t WHERE x = 81 AND y >= 1037 ORDER BY x ASC, y DESC LIMIT 5
query: SELECT * FROM t WHERE x < 2698 ORDER BY x ASC LIMIT 5
query: SELECT * FROM t WHERE x = 1503 AND y = 554 AND z >= 185 ORDER BY x DESC, y DESC, z DESC LIMIT 5
query: SELECT * FROM t WHERE x = 619 AND y > 1414 ORDER BY x DESC, y ASC LIMIT 5
query: SELECT * FROM t WHERE x >= 865 ORDER BY x DESC LIMIT 5
query: SELECT * FROM t WHERE x = 1596 AND y = 622 AND z = 62 ORDER BY x DESC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x = 1555 AND y = 1257 AND z < 1929 ORDER BY x ASC, y ASC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x > 2598 LIMIT 5
query: SELECT * FROM t WHERE x = 302 AND y = 2476 AND z < 2302 ORDER BY z DESC LIMIT 5
query: SELECT * FROM t WHERE x = 2197 AND y = 2195 AND z > 2089 ORDER BY y ASC, z DESC LIMIT 5
query: SELECT * FROM t WHERE x = 1030 AND y = 1717 AND z < 987 LIMIT 5
query: SELECT * FROM t WHERE x = 2899 AND y >= 382 ORDER BY y DESC LIMIT 5
query: SELECT * FROM t WHERE x = 62 AND y = 2980 AND z < 1109 ORDER BY x DESC, y DESC, z DESC LIMIT 5
query: SELECT * FROM t WHERE x = 550 AND y > 221 ORDER BY y DESC LIMIT 5
query: SELECT * FROM t WHERE x = 376 AND y = 1874 AND z < 206 ORDER BY y DESC, z ASC LIMIT 5
query: SELECT * FROM t WHERE x = 859 AND y = 2157 ORDER BY x DESC LIMIT 5
query: SELECT * FROM t WHERE x = 2166 AND y = 2079 AND z < 301 ORDER BY x DESC, y ASC LIMIT 5
```
the queries are run against both sqlite and limbo.
Reviewed-by: Pere Diaz Bou (@pereman2)
Reviewed-by: Preston Thorpe (@PThorpe92)
Closes#1330
First attempt at closing #1212. Also with this PR, I added the option of
using `with` syntax for `TestLimboShell`. It automatically closes the
shell on error, and facilitates error handling overall. If this is
merged, I can update the other python tests to use `with` as well.
Reviewed-by: Preston Thorpe (@PThorpe92)
Closes#1230
Some more helper utilities extracted out from #1351 to make the surface
area of that PR smaller
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Closes#1353
Apply affinities to a range of P2 registers starting with P1.
P4 is a string that is P2 characters long. The N-th character of the string indicates the column affinity that should be used for the N-th memory cell in the range.
If P4==0 then register P3 holds a blob constructed by MakeRecord. If P4>0 then register P3 is the first of P4 registers that form an unpacked record.
Cursor P1 is on an index btree. If the record identified by P3 and P4 is not the prefix of any entry in P1 then a jump is made to P2. If P1 does contain an entry whose prefix matches the P3/P4 record then control falls through to the next instruction and P1 is left pointing at the matching entry.
This operation leaves the cursor in a state where it cannot be advanced in either direction. In other words, the Next and Prev opcodes do not work after this operation.
