What is Difference between ExecuteNonQuery, ExecuteScalar and ExecuteReader ?

ExecuteNonQuery

ExecuteNonQuery method will return number of rows effected with INSERT, DELETE or UPDATE operations.This ExecuteNonQuery method will be used only for insert, update and delete, Create, and SETstatements.

ExecuteScalar

Execute Scalar will return single row single column value i.e. single value, on execution of SQL Query or Stored procedure using command object. It’s very fast to retrieve single values from database.


ExecuteReader

Execute Reader will be used to return the set of rows, on execution of SQL Query or Stored procedure using command object. This one is forward only retrieval of records and it is used to read the table values from first to last.


Difference between char varchar and nvarchar in sql server?

Char DataType

Char datatype which is used to store fixed length of characters. Suppose if we declared char(50) it will allocates memory for 50 characters. Once we declare char(50) and insert only 10 characters of word then only 10 characters of memory will be used and other 40 characters of memory will be wasted.

varchar DataType

Varchar means variable characters and it is used to store non-unicode characters. It will allocate the memory based on number characters inserted. Suppose if we declared varchar(50) it will allocates memory of 0 characters at the time of declaration. Once we declare varchar(50) and insert only 10 characters of word it will allocate memory for only 10 characters.

nvarchar DataType

nvarchar datatype same as varchar datatype but only difference nvarchar is used to store Unicode characters and it allows you to store multiple languages in database. nvarchar datatype will take twice as much space to store extended set of characters as required by other languages.