Error oracle- ORA-00001: unique constraint (string.string) violated

ORA-00001:  unique constraint (string.string) violated

Cause:     An UPDATE or INSERT statement attempted to insert a duplicate key. For Trusted Oracle configured in DBMS MAC mode, you may see this message if a duplicate entry exists at a different level.

Action:     Either remove the unique restriction or do not insert the key.

Error oracle- ORA-00000- normal, successful completion

ORA-00000:   normal, successful completion   

Cause:     Normal exit.

Action:     None.

Error oracle- ORA-00904: string: invalid identifier

Cause:    The column name entered is either missing or invalid.

Action:    Enter a valid column name. A valid column name must begin with a letter, be less than or equal to 30 characters, and consist of only alphanumeric characters and the special characters $, _, and #. If it contains other characters, then it must be enclosed in double quotation marks. It may not be a reserved word.