5.9. Schemas #

A Postgres Pro database cluster contains one or more named databases. Roles and a few other object types are shared across the entire cluster. A client connection to the server can only access data in a single database, the one specified in the connection request.


Users of a cluster do not necessarily have the privilege to access every database in the cluster. Sharing of role names means that there cannot be different roles named, say, joe in two databases in the same cluster; but the system can be configured to allow joe access to only some of the databases.

A database contains one or more named schemas, which in turn contain tables. Schemas also contain other kinds of named objects, including data types, functions, and operators. The same object name can be used in different schemas without conflict; for example, both schema1 and myschema can contain tables named mytable. Unlike databases, schemas are not rigidly separated: a user can access objects in any of the schemas in the database they are connected to, if they have privileges to do so.

There are several reasons why one might want to use schemas:

  • To allow many users to use one database without interfering with each other.

  • To organize database objects into logical groups to make them more manageable.

  • Third-party applications can be put into separate schemas so they do not collide with the names of other objects.

Schemas are analogous to directories at the operating system level, except that schemas cannot be nested.

5.9.1. Creating a Schema #

To create a schema, use the CREATE SCHEMA command. Give the schema a name of your choice. For example:


To create or access objects in a schema, write a qualified name consisting of the schema name and table name separated by a dot:


This works anywhere a table name is expected, including the table modification commands and the data access commands discussed in the following chapters. (For brevity we will speak of tables only, but the same ideas apply to other kinds of named objects, such as types and functions.)

Actually, the even more general syntax


can be used too, but at present this is just for pro forma compliance with the SQL standard. If you write a database name, it must be the same as the database you are connected to.

So to create a table in the new schema, use:

CREATE TABLE myschema.mytable (

To drop a schema if it's empty (all objects in it have been dropped), use:

DROP SCHEMA myschema;

To drop a schema including all contained objects, use:


See Section 5.14 for a description of the general mechanism behind this.

Often you will want to create a schema owned by someone else (since this is one of the ways to restrict the activities of your users to well-defined namespaces). The syntax for that is:

CREATE SCHEMA schema_name AUTHORIZATION user_name;

You can even omit the schema name, in which case the schema name will be the same as the user name. See Section 5.9.7 for how this can be useful.

Schema names beginning with pg_ are reserved for system purposes and cannot be created by users.

5.9.2. The Public Schema #

In the previous sections we created tables without specifying any schema names. By default such tables (and other objects) are automatically put into a schema named public. Every new database contains such a schema. Thus, the following are equivalent:

CREATE TABLE products ( ... );


CREATE TABLE public.products ( ... );

5.9.3. The vault Schema #

Postgres Pro provides an enhanced security mechanism that allows you to protect sensitive data against unauthorized access of malicious users who can read or even modify such data and stay undetected. This is achieved by creating the vault schema and designating a separate user called security officer who manages access to the schema and its objects. In this case, the schema owner is only responsible for the management of schema objects. You must be a superuser to set the security officer for a schema. To set the roles and create the vault schema, follow the procedure below:

  1. Create a user for the vault schema owner and remember to set a password for this user.

    CREATE USER vault_owner WITH LOGIN;
    GRANT CONNECT ON DATABASE database_name TO vault_owner;

  2. Create a user for the security officer of the vault schema and remember to set a password for this user.

    CREATE USER vault_security_officer WITH LOGIN;
    GRANT CONNECT ON DATABASE database_name TO vault_security_officer;

  3. Create the vault schema, assign its owner, and set the security officer.

    CREATE SCHEMA vault_name;
    ALTER SCHEMA vault_name OWNER TO vault_owner;
    ALTER SCHEMA vault_name SECURITY OFFICER TO vault_security_officer;

The security officer is the only non-superuser who can GRANT or REVOKE privileges to access the vault schema and its objects, more specifically pg_class, pg_proc, pg_type, and pg_collation. This cannot be done by the schema owner or the object owner.

Postgres Pro also enables you to create the vault schema out of the existing schema by setting the security officer for it. To set the security officer, use the ALTER SCHEMA command.

Once the vault schema, its owner, and security officer are created, the superuser login is disabled. After that, only the schema owner and the schema security officer can manage the data and access to it, respectively. Also, no other user of the server has ADMIN OPTION on them.

5.9.4. The Schema Search Path #

Qualified names are tedious to write, and it's often best not to wire a particular schema name into applications anyway. Therefore tables are often referred to by unqualified names, which consist of just the table name. The system determines which table is meant by following a search path, which is a list of schemas to look in. The first matching table in the search path is taken to be the one wanted. If there is no match in the search path, an error is reported, even if matching table names exist in other schemas in the database.

The ability to create like-named objects in different schemas complicates writing a query that references precisely the same objects every time. It also opens up the potential for users to change the behavior of other users' queries, maliciously or accidentally. Due to the prevalence of unqualified names in queries and their use in Postgres Pro internals, adding a schema to search_path effectively trusts all users having CREATE privilege on that schema. When you run an ordinary query, a malicious user able to create objects in a schema of your search path can take control and execute arbitrary SQL functions as though you executed them.

The first schema named in the search path is called the current schema. Aside from being the first schema searched, it is also the schema in which new tables will be created if the CREATE TABLE command does not specify a schema name.

To show the current search path, use the following command:

SHOW search_path;

In the default setup this returns:

 "$user", public

The first element specifies that a schema with the same name as the current user is to be searched. If no such schema exists, the entry is ignored. The second element refers to the public schema that we have seen already.

The first schema in the search path that exists is the default location for creating new objects. That is the reason that by default objects are created in the public schema. When objects are referenced in any other context without schema qualification (table modification, data modification, or query commands) the search path is traversed until a matching object is found. Therefore, in the default configuration, any unqualified access again can only refer to the public schema.

To put our new schema in the path, we use:

SET search_path TO myschema,public;

(We omit the $user here because we have no immediate need for it.) And then we can access the table without schema qualification:

DROP TABLE mytable;

Also, since myschema is the first element in the path, new objects would by default be created in it.

We could also have written:

SET search_path TO myschema;

Then we no longer have access to the public schema without explicit qualification. There is nothing special about the public schema except that it exists by default. It can be dropped, too.

See also Section 9.26 for other ways to manipulate the schema search path.

The search path works in the same way for data type names, function names, and operator names as it does for table names. Data type and function names can be qualified in exactly the same way as table names. If you need to write a qualified operator name in an expression, there is a special provision: you must write


This is needed to avoid syntactic ambiguity. An example is:

SELECT 3 OPERATOR(pg_catalog.+) 4;

In practice one usually relies on the search path for operators, so as not to have to write anything so ugly as that.

5.9.5. Schemas and Privileges #

By default, users cannot access any objects in schemas they do not own. To allow that, the owner of the schema must grant the USAGE privilege on the schema. By default, everyone has that privilege on the schema public. To allow users to make use of the objects in a schema, additional privileges might need to be granted, as appropriate for the object.

A user can also be allowed to create objects in someone else's schema. To allow that, the CREATE privilege on the schema needs to be granted. In databases upgraded from PostgreSQL 14 or earlier, everyone has that privilege on the schema public. Some usage patterns call for revoking that privilege:


(The first public is the schema, the second public means every user. In the first sense it is an identifier, in the second sense it is a key word, hence the different capitalization; recall the guidelines from Section 4.1.1.)

5.9.6. The System Catalog Schema #

In addition to public and user-created schemas, each database contains a pg_catalog schema, which contains the system tables and all the built-in data types, functions, and operators. pg_catalog is always effectively part of the search path. If it is not named explicitly in the path then it is implicitly searched before searching the path's schemas. This ensures that built-in names will always be findable. However, you can explicitly place pg_catalog at the end of your search path if you prefer to have user-defined names override built-in names.

Since system table names begin with pg_, it is best to avoid such names to ensure that you won't suffer a conflict if some future version defines a system table named the same as your table. (With the default search path, an unqualified reference to your table name would then be resolved as the system table instead.) System tables will continue to follow the convention of having names beginning with pg_, so that they will not conflict with unqualified user-table names so long as users avoid the pg_ prefix.

5.9.7. Usage Patterns #

Schemas can be used to organize your data in many ways. A secure schema usage pattern prevents untrusted users from changing the behavior of other users' queries. When a database does not use a secure schema usage pattern, users wishing to securely query that database would take protective action at the beginning of each session. Specifically, they would begin each session by setting search_path to the empty string or otherwise removing schemas that are writable by non-superusers from search_path. There are a few usage patterns easily supported by the default configuration:

  • Constrain ordinary users to user-private schemas. To implement this pattern, first ensure that no schemas have public CREATE privileges. Then, for every user needing to create non-temporary objects, create a schema with the same name as that user, for example CREATE SCHEMA alice AUTHORIZATION alice. (Recall that the default search path starts with $user, which resolves to the user name. Therefore, if each user has a separate schema, they access their own schemas by default.) This pattern is a secure schema usage pattern unless an untrusted user is the database owner or has been granted ADMIN OPTION on a relevant role, in which case no secure schema usage pattern exists.

    In PostgreSQL 15 and later, the default configuration supports this usage pattern. In prior versions, or when using a database that has been upgraded from a prior version, you will need to remove the public CREATE privilege from the public schema (issue REVOKE CREATE ON SCHEMA public FROM PUBLIC). Then consider auditing the public schema for objects named like objects in schema pg_catalog.

  • Remove the public schema from the default search path, by modifying postgresql.conf or by issuing ALTER ROLE ALL SET search_path = "$user". Then, grant privileges to create in the public schema. Only qualified names will choose public schema objects. While qualified table references are fine, calls to functions in the public schema will be unsafe or unreliable. If you create functions or extensions in the public schema, use the first pattern instead. Otherwise, like the first pattern, this is secure unless an untrusted user is the database owner or has been granted ADMIN OPTION on a relevant role.

  • Keep the default search path, and grant privileges to create in the public schema. All users access the public schema implicitly. This simulates the situation where schemas are not available at all, giving a smooth transition from the non-schema-aware world. However, this is never a secure pattern. It is acceptable only when the database has a single user or a few mutually-trusting users. In databases upgraded from PostgreSQL 14 or earlier, this is the default.

For any pattern, to install shared applications (tables to be used by everyone, additional functions provided by third parties, etc.), put them into separate schemas. Remember to grant appropriate privileges to allow the other users to access them. Users can then refer to these additional objects by qualifying the names with a schema name, or they can put the additional schemas into their search path, as they choose.

5.9.8. Portability #

In the SQL standard, the notion of objects in the same schema being owned by different users does not exist. Moreover, some implementations do not allow you to create schemas that have a different name than their owner. In fact, the concepts of schema and user are nearly equivalent in a database system that implements only the basic schema support specified in the standard. Therefore, many users consider qualified names to really consist of user_name.table_name. This is how Postgres Pro will effectively behave if you create a per-user schema for every user.

Also, there is no concept of a public schema in the SQL standard. For maximum conformance to the standard, you should not use the public schema.

Of course, some SQL database systems might not implement schemas at all, or provide namespace support by allowing (possibly limited) cross-database access. If you need to work with those systems, then maximum portability would be achieved by not using schemas at all.