I'd really appreciate if you could clarify this to me. Let's say I have a table named TABLE_A that is a bridge to many-to-many relationship between TABLE_B and TABLE_C, as such here is my declaration:
CREATE TABLE table_a ( table_b_id INT4 NOT NULL REFERENCES table_b ON DELETE CASCADE ON UPDATE CASCADE,
table_c_id INT4 NOT NULL REFERENCES table_c ON DELETE RESTRICT ON UPDATE CASCADE,
This will automatically create a unique index on the primary key.
Yes it will. Primary keys in PostgreSQL are implemented using unique indexes, one may say.
Well, if I do a query later like: select * from table_a where table_b_id=1, will the query use an index? Will this be true when I do join on this table?
The short answer is: yes.
The longer answer is: yes, when planner sees that the index is the most efficient way to approach given query. In some cases using sequentional scan may be more efficient.
Try EXPLAIN ANALYZE SELECT ...; -- it will tell you what did the planer choose.
