Difference between ExecuteNonQuery() and EXecuteReader()

ExecuteReader

Do not use: when database query is going to provide for sure exactly 1 record. It may be getting record by its id (which is PK in the database) - GetOrderById and such. In this case use ExecuteNonQuery with output parameters.

Use: when database query is going to provide a set of records. It may be search or report.

ExecuteNonQuery

Use: when we are talking about a single database record - in Update, Insert, Delete and Get by Id. In all these cases we can use input/output/input-output parameters. Please note that from the application architecture point of view it is also good practices when your Insert and Update stored procedure returns changed record exactly like Get By Id method does.

ExecuteNonQuery():
When the command object is representing DML statments/DDL statments/Stored subprogram then we can go with executenonquery method

ExecuteReader():
When the Select statment returns more than one value then we can go with ExecuteReader()