Yes I'm sure.

With the left join FB does a full scan on Table_A and uses the Foreign Key index on Table_B. The index on table_B.field_B is not used at all.

So you get millions of reads if the table contains millions of data

With the inner join the index on  table_B.field_B is used and you only get 1 read (if It's only 1 row that matches the condition)

Is it possible to force the optimizer tu use the index on table_B.field_B?

Regards
Carsten

 

Are you sure that this query looks like this?

 

For me such query use indexes in both cases left and inner.

Show full example with plans

 

Regards,

Karol Bieniaszewski