- If a required field in a table is not contained in the view
- SQL to create view has GROUP BY
- SQL to create view has aggregation
- SQL to create view uses DISTINCT
- SQL to create view has more than one table (through a join)
Indexes are objects to make queries run faster. The WHERE clause and ORDER BY clause will specifically benefit from some indexes. They cannot be placed on columns of type LOB or RAW. You automatically get an index for a primary key or a unique column. The optimizer might use an index for almost everything except for NOT EQUALS comparisons. A composite index has two or more columns in it.
Finally synonyms are aliases for database objects. They can be for tables, views, sequences, or even other synonyms. The object referenced does not even have to exist when you create the synonym. But it must by the itme you use it. There are two types of synoyms: