Ref keyword is used to pass reference of an data type value (address of value) to the called function, its similar to the concept of pass by reference of c,java language. There are basically 2 types of indexes 1)CLustered-Index: which is generally auto-index created by sql when we a primary column defined(we can change this to any other column manually). 2) Non-clustered Index: We can define non-clustered index on any of the existing columns of a table. There can only be 1 clustered index and multiple non-clustered index on one table. Using simple joins or correlated queries update statement we can change column data from other table