 tbl0.t0_pk is a primary key. tbl0.t0_fk_t0_pk is a foreign key on that t0_pk column.  Explain plan on a database with 00,000 rows in tbl0 and 0000 rows in tbl0 shows that it's doing a full table scan on tbl0. Seems to me that it should be faster if it could do a index query on tbl0. Explain plan on a database with 00,000 rows in tbl0 and 0000 rows in tbl0 shows that it's doing a full table scan on tbl0. Seems to me that it should be faster if it could do a index query on tbl0. 