Hello,

there are two more points:

1. The statements that create the sample indices should have been:

create unique index IDX_T11 on T1 (s1);
create unique index IDX_T12 on T2 (s1);

2. We have tested these sample statements for other Firebird versions

Under

* Firebird 1.5.6 and
* Firebird 2.0.4

the index is taken for the LEFT-JOIN statement. The performance of the original statement on the larger tables is okay for Firebird 2.0.4 as well.

For the

* Firebird 2.1.4 - Snapshot and
* the Firebird 2.5 RC2

the index is not taken for the simplified version and the statement on the original tables.

Greetings

Andreas