Difference Between IN and EXISTS

	IN	EXIST
1	IN is faster than EXISTS, when the sub-query results is very small.	EXISTS is much faster than IN, when the sub-query results is very large.
2	IN can't compare anything with null, so it has no result for null. For Example:Select * from Table where Table_ID in (select null) Above one would return empty.	EXISTS can compare everything with null. Select *  from Table where exists (select null). Above query will return all the records
3	If you are using the IN operator, the SQL engine will scan all records fetched from the inner query	On the other hand if we are using EXISTS, the SQL engine will stop the scanning process as soon as it found a match.
4	If Most of the filter criteria is in subquery then better to use IN	If most of the filter criteria is in main query then better to use EXISTS.

Difference Between VIEW and Materialized View

View	Materialized view
1.  In Views query result is not stored in the disk or database.	1. Materialized view allows to store query result in disk or table.
2. When we create view using any table, rowid of view is same as original table.	2. In case of Materialized view rowid is different.
3.  In case of View we always get latest data.	3. Materialized view we need to refresh the view for getting latest data.
4. In case of view we don't need extra trigger or some automatic method to refresh the view.	4. In case of Materialized view we need extra trigger or some automatic method so that we can keep Materialized view refreshed.

Difference Between CASE and DECODE

CASE	DECODE
1.CASE expression complies with ANSI SQL	1. DECODE is specific to Database vendors (like Oracle, SQL Server)
2. Case can compare discrete as well as Range value	2. DECODE compare discrete values not Range
3. CASE can work with logical operators, predicates and searchable subqueries.	3. DECODE can work with only scaler values
4. CASE is a statement.	4. DECODE is a function.
5. CASE expects datatype consistency.	5. DECODE does not expects datatype consistency.