PostgreSQL currently has 19 query operators.
Seq Scan operator is the most basic query operator. Any single-table query can be carried out using the
Seq Scan operator.
Index Scan operator works by traversing an index structure. If you specify a starting value for an indexed column (
WHERE record_id >= 1000, for example), the
Index Scan will begin at the appropriate value. If you specify an ending value (such as
WHERE record_id < 2000), the
Index Scan will complete as soon as it finds an index entry greater than the ending value.
Sort operator imposes an ordering on the result set. PostgreSQL uses two different sort strategies: an in-memory sort and an on-disk sort. You can tune a PostgreSQL instance by adjusting the value of the
work_mem runtime parameter.
UNIQUE operator eliminates duplicate values from the input set. The input set must be ordered by the columns, and the columns must be unique.