Question

 SqlConnection connection = new SqlConnection(connString.ToString());
    string select = "SELECT (CASE WHEN MAX(page_no) IS NULL  THEN 1 ELSE MAX(page_no)+1 END) FROM dbo.BOOK";
    string insert = "INSERT INTO dbo.BOOK (book_id,select) VALUES (121,4)";
    SqlCommand sqlCommand = new SqlCommand(insert,connection);
    insert.ExecuteNonQuery();

Here I got exception where the insert contains invalid string select.
Please tell me how assign sub query within the insert?

Answer 1

you cannot use a select statement like this
if you want to use a sub query it has to be in single statement

but in above statement you write in different different statement for selection
and insert query .

so cmd.ExecuteNonquery() execute only insert text statement so SQL engine unable to find SELECT(and SELECT is a Reserved keyword) so it gives you a error

if you go with subquery try this

SqlConnection connection = new SqlConnection(connString.ToString());

string select = "SELECT 121, (CASE WHEN MAX(page_no) IS NULL  THEN 1 ELSE MAX(page_no)+1 END) FROM dbo.BOOK";
string insert = "INSERT INTO dbo.BOOK (book_id,[select]) "+select;

SqlCommand sqlCommand = new SqlCommand(insert,connection);

sqlCommand.ExecuteNonQuery();