execute reader

Execute Non query

Scalar Bcoz it return's only 1 result that's why scalar.

Reader... Bcoz It read the data directly from the database

Execute Scalar

Execute scalar  is faster so it is execute one row at the 
time

execute non query

most of the above answers are wrong

write answer is execute reader

execute reader is fast

Execute Reader is faster it
 internally  stores result of a query as an array.

Excute reader is to easy and quickly fetch the data from 
database. but in some casse excute non query is more useful 
than excute query , excute reader and excute scalar


thanks

Execue reader

Wrong Question , As ExceuteReader(),ExecuteNonQuery() and
ExecuteScaler() interact to database in same manner and we
all Know about the ExceuteReader(),ExecuteNonQuery() and
ExecuteScaler() serves for different purpose , as
ExceuteReader() reads data against select query , 
ExecuteScaler() reads single cell value and
ExecuteNonQuery() used for action query not returns any
result set.

ExecuteNonQuery is used to inserts, updates, deletes.
ExecuteScaler is used to return values at a stretch; and 
can do data modifications too.
ExecuteReader is forward only reading of row by row.

The number of readers that can be open at a time has 
limitation (255)

Execute Scaler has no such restriction.  You can use 
sqlparameters (output) to get more than one field value,
you can use multiple queries to get more than one result.

Because of less overheads, ExecuteReader has a slight 
performance advantage but has limitations.

Do not forget to close Readers!

execute reader

Scalar will be faster that the execute reader and execute 
non query. As scalar only fetch one column single row. 
Whereas execute reader may return numbers of record and 
though non-query will not return any records it will take 
time to identify the data types to validate be4 inserting 
the data