We’ve found a bug where creating indexes on expressions causes a query to give
incorrect results. Our indexes use some complex custom functions, but the bug
is easy to reproduce just using the ‘abs’ function:
SELECT * FROM docs WHERE abs(a)=2 OR abs(b)=9
After indexing ‘abs(a)’ and ‘abs(b)’, this query no longer returns correct
results.
This seems related to the OR — if we query only abs(a)=2, or only abs(b)=9, it
works correctly.
The transcript below comes from the SQLite 3.24 shell.
### Populate database:
sqlite> create table docs (a int, b int);
sqlite> insert into docs (a, b) values (2, 4);
sqlite> insert into docs (a, b) values (3, 9);
### Simple OR query that correctly matches both docs:
sqlite> select * from docs where abs(a)=2 or abs(b)=9;
a = 2
b = 4
a = 3
b = 9
sqlite> explain query plan select * from docs where abs(a)=2 or abs(b)=9;
QUERY PLAN
`--SCAN TABLE docs
### Create indexes on the two expressions in the above query:
sqlite> create index ia on docs (abs(a));
sqlite> create index ib on docs (abs(b));
### Now repeat the query — it incorrectly finds only one doc, and the query
plan looks bogus:
sqlite> select * from docs where abs(a)=2 or abs(b)=9;
a = 3
b = 9
sqlite> explain query plan select * from docs where abs(a)=2 or abs(b)=9;
QUERY PLAN
`--SEARCH TABLE docs USING INDEX ib (<expr>=?)
# And here’s the full explanation with bytecodes:
sqlite> explain select * from docs where abs(a)=2 or abs(b)=9;
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 23 0 00 Start at 23
1 OpenRead 0 2 0 2 00 root=2 iDb=0; docs
2 OpenRead 1 3 0 k(2,,) 02 root=3 iDb=0; ib
3 Once 0 11 0 00
4 OpenEphemeral 3 1 0 k(1,) 00 nColumn=1
5 Integer 2 2 0 00 r[2]=2
6 MakeRecord 2 1 3 A 00 r[3]=mkrec(r[2])
7 IdxInsert 3 3 2 1 00 key=r[3]
8 Integer 9 2 0 00 r[2]=9
9 MakeRecord 2 1 3 A 00 r[3]=mkrec(r[2])
10 IdxInsert 3 3 2 1 00 key=r[3]
11 Rewind 3 22 0 00
12 Column 3 0 1 00 r[1]=
13 IsNull 1 21 0 00 if r[1]==NULL goto
21
14 SeekGE 1 21 1 1 00 key=r[1]
15 IdxGT 1 21 1 1 00 key=r[1]
16 DeferredSeek 1 0 0 00 Move 0 to 1.rowid
if needed
17 Column 0 0 4 00 r[4]=docs.a
18 Column 0 1 5 00 r[5]=docs.b
19 ResultRow 4 2 0 00 output=r[4..5]
20 Next 1 15 0 00
21 NextIfOpen 3 12 0 00
22 Halt 0 0 0 00
23 Transaction 0 0 7 0 01 usesStmtJournal=0
24 Goto 0 1 0 00
—Jens
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