Every database offers various schema objects, referred as database objects. Working with a database requires you to know the following.

• Database objects
• SQL Statement and Clauses
• Writing SQL query

During migration from Oracle to PostgreSQL, you must first know what Oracle database objects are supported in PostgreSQL and to what extent Oracle SQL and PostgreSQL are different.

This chapter describes you high level overview of Oracle to PostgreSQL differences.

ORACLE	POSTGRESQL
TABLE	TABLE
VIEW	VIEW
CONSTRAINT (Primary Key, Foreign Key, Unique Key, Check)	CONSTRAINT (Primary Key, Foreign Key, Unique Key, Check)
INDEX	INDEX
MATERIALIZED VIEW	MATERIALIZED VIEW
SEQUENCE	SEQUENCE
SYNONYM	Not available in PostgreSQL. Ignored in PostgreSQL, but can be partially achieved through Views. SET search_path can also be a work-around for synonyms.
TYPE	DOMAIN/ TYPE
COLLECTION TYPES	Not available in PostgreSQL. Can be achieved through Arrays in PostgreSQL.
STORED FUNCTION	FUNCTION
STORED PROCEDURE	Procedures are available in PostgreSQL 11 onwards.
PACKAGE	Not available in PostgreSQL. Achieved through creating individual schemas.
TRIGGER	TRIGGER

Object DDL differences

Schema objects (such as views, synonyms, constraints, indexes, functions, procedures) in Oracle database can be either in valid or invalid state. But in PostgreSQL, objects other than indexes do not have any status associated. All objects once compiled are always in valid state.

Oracle and PostgreSQL work quite differently in that respect: