Differences Between Execution Query, Execute Scalar and Execute Reader.

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 SET statements. 

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. MOSTLY HELPFUL WHEN SEARCHNG FOR EXISTANCE OF PARTICULAR DATABASE RECORDS.since its only for searching and retrieval of records here as well INSERT, DELETE or UPDATE queries for its operations tobe performed is not applicable.

Execute Scalar

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. as comapred to executeNonquery its not depended on INSERT, DELETE or UPDATE queries for its operations tobe performed.