SQL adaptation guide For Oracle Database 9.2, 10.x, 11.x, 12x / Data dictionary |
Informix | ORACLE |
---|---|
CREATE TABLE emp ( ... emp_code CHAR(10) UNIQUE CONSTRAINT pk_emp, |
CREATE TABLE emp ( ... emp_code CHAR(10) CONSTRAINT pk_emp UNIQUE, ... |
Like Informix, ORACLE creates an index to enforce PRIMARY KEY constraints (some RDBMS do not create indexes for constraints). Using "CREATE UNIQUE INDEX" to define unique constraints is obsolete (use primary keys or a secondary key instead).
Like Informix, ORACLE creates an index to enforce UNIQUE constraints (some RDBMS do not create indexes for constraints).
When using a unique constraint, Informix allows only one row with a NULL value, while ORACLE allows several rows with NULL! Using CREATE UNIQUE INDEX is obsolete.
The check condition may be any valid expression that can be evaluated to TRUE or FALSE, including functions and literals. You must verify that the expression is not Informix specific.
The database interface does not convert constraint naming expressions when creating tables from BDL programs. Review the database creation scripts to adapt the constraint naming clauses for ORACLE.