Name resolution of SQL objects

Informix®

Informix uses the following form to identify an SQL object:

database[@dbservername]:][{owner|"owner"}.]identifier

The ANSI convention is to use double quotes for identifier delimiters (For example: "customer"."cust_name").

Informix database object names are not case-sensitive in non-ANSI databases. When using double-quoted identifiers, Informix becomes case sensitive.

With non-ANSI Informix databases, you do not have to give a schema name before the tables when executing an SQL statement:

SELECT ... FROM customer WHERE ...

In Informix ANSI compliant databases:

The table name must include "owner", unless the connected user is the owner of the database object.
The database server shifts the owner name to uppercase letters before the statement executes, unless the owner name is enclosed in double quotes.

PostgreSQL

With PostgreSQL, a database object name takes the following form:

[[database.]schema.]identifier

You can define a list of schemas to be searched when the database object is not qualified. The list of schemas to look in is specified with SET search_path TO schema-1,schema-2,... for an SQL session (it can also be defined at the database level and user definition level).

When creating a table without a schema prefix, the table is created in the "public" schema. This schema is listed in the search path by default.

Solution

To write portable SQL, regarding database object names:

Use simple database object names (without any owner/schema prefix)
Do not use double quotes to surround database object identifiers.
If needed, define public synonyms to reference database objects in others databases/schema.
Specify database object identifiers in lowercase.