Hello,
I've just wanted to ask about using covering indexes for scans. A very
rudimentary test:
create table t (c1,c2, c3, c4);
create index idxtc1 on t(c1);
The simple "select" scans the full table:
explain query plan select c1 from t;
SCAN TABLE t (~1000000 rows)
A select with a dummy "order by" uses the covering index:
explain query plan select c1 from t order by c1;
SCAN TABLE t USING COVERING INDEX idxtc1 (~1000000 rows)
It seems to me that using a covering index scan would always be faster
in both cases (fewer disk page reads). Am i wrong? Is there a reason for
SQLite to not use a covering index for scans?
Thank you in advance,
lefteris
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