Differents between ExecuteReader, ExecuteNonQuery & ExecuteScalar

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ExecuteReader : Use for accessing data. It provides a forward-only, read-only, connected recordset.

ExecuteNonQuery : Use for data manipulation, such as Insert, Update, Delete.

ExecuteScalar : Use for retriving 1 row 1 col. value.,
i.e. Single value.
eg: for retriving aggregate function.
It is faster than other ways of retriving a single value from DB.

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