Build Phase: A Hash table is built using the inner relation records.

The join in the above example is just a Cartesian product of both tables. Since the join clause is “ Seq Scan on blogtable1 (cost=0.00.145.00 rows=10000 width=8) The Join between relation A and B with condition A.ID Seq Scan on blogtable1 bt1 (cost=0.00.145.00 rows=10000 width=8) Nested Loop Join (NLJ) is the simplest join algorithm wherein each record of outer relation is matched with each record of inner relation. In all our subsequent examples, we consider default configuration parameter unless otherwise specified specifically. Postgres=# insert into blogtable2 values(generate_series(1,1000),3) Postgres=# insert into blogtable1 values(generate_series(1,10000),3) Postgres=# create table blogtable2(id1 int, id2 int) postgres=# create table blogtable1(id1 int, id2 int) Let’s create some pre-setup table and populate with some data, which will be used frequently to better explain these scan methods. These join methods are implemented by most of the relational databases. query, table data, join clause, selectivity, memory etc. PostgreSQL supports the below kind of joins:Įach of these Join methods are equally useful depending on the query and other parameters e.g.

Inner join example postgresql