Mastering PostgreSQL 12 - Third Edition

Applying table constraints

What happens if filters are applied to the table? What will the optimizer decide to do in order to execute this query in the most efficient way possible? The following example shows us how the PostgreSQL planner will behave:

test=# EXPLAIN SELECT * FROM t_data WHERE t = '2016-01-04';                            QUERY PLAN -----------------------------------------------------------------  Append (cost=0.00..95.12 rows=23 width=40)    -> Seq Scan on t_data (cost=0.00..0.00 rows=1 width=40)          Filter: (t = '2016-01-04'::date)    -> Seq Scan on t_data_2016 (cost=0.00..25.00 rows=6 width=40)          Filter: (t = '2016-01-04'::date)    -> Seq Scan on t_data_2015 (cost=0.00..25.00 rows=6 width=40)          Filter: (t = '2016-01-04'::date)  -> Seq Scan on t_data_2014 (cost=0.00..25.00 ...