Portable SQL/Common/DBMS Differences

Differences between implementations

NULL in column definition

This table is originally from "Building Truly Portable Database Applications in PHP": NULL

Database	Default value	Definition allowed	Notes
Firebird	NULL	no
MySQL	NULL	yes
Oracle	NULL	yes	Empty strings considered NULL
PostgreSQL	NULL	yes
SQL Server	NOT NULL	yes
SQLite	NULL	yes
Sybase ASE	NOT NULL	yes

The "Definition allowed" column indicates if specifying NULL in table column definitions is allowed for CREATE TABLE statements - NOT NULL is always allowed. If "yes", the following statement doesn't generate an error:

CREATE TABLE mytable ( id INTEGER NULL )

Identifier case

This table is originally from "Building Truly Portable Database Applications in PHP": Column Name Case

Database	Case	Notes
Firebird	upper	preserved when using double quotes (")
MySQL	preserved
Oracle	upper
PostgreSQL	lower
SQL Server	preserved
SQLite	preserved
Sybase ASE	preserved

Since OpenDBX 1.1.4 the use of double quotes (") for identifiers (table and column names) is suggested. This complies to ANSI standards and is the only way to use reserved words and prevent clashes in the future if language constructs are extended by the database vendors.