ASP.NET PDF Viewer using C#, VB/NET

First, form a Cartesian product of the employee and dept tables. Next, see which of the rows in the Cartesian product satisfies the requirement. Here s the query: WHERE e.job=supervisor AND d.dept=operations AND e.dept_no=d.dept_no. The following would be the total cost of performing the query: The Cartesian product of employee and dept requires a read of both tables: 2,000 + 40 = 2,040 reads Creating the Cartesian product: 2,000 * 40 = 80,000 writes Reading the Cartesian product to compare against the select condition: 2,000 * 40 = 80,000 reads Total I/O cost: 2,040 + 80,000 + 80,000 = 162,040

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The second query uses a join of the employee and dept tables. First, join the employee and dept tables on the dept_no column. From this join, select all rows where e.job=supervisor and city=Dallas. The following would be the total cost of performing the query: Joining the employee and dept tables first requires a read of all the rows in both tables: 2,000 + 40 = 2,040 Creating the join of the employee and dept tables: 2,000 writes Reading the join results costs: 2,000 reads Total I/O cost: 2,040 + 2,000 + 2,000 = 6,040

The following output results:

The third query also uses a join of the employee and dept tables, but not all the rows in the two tables only selected rows from the two tables are joined. Here s how this query would proceed to

throw gcnew ArgumentNullException("obj"); // determine the type of the object Type^ t = obj->GetType(); // determine the MethodInfo object for the target method MethodInfo^ mi = t->GetMethod(function); if (!mi) throw gcnew ArgumentException("Function does not exist"); return mi->Invoke(obj, args); } For the argument args, zero or more arguments of any tracking handle type and of any managed value type can be passed. Managed values passed will be boxed, and the Object^ element in the args array will refer to the boxed value. If a function is compiled to native code, or if you want to allow native callers for your function, you have to use the old C-style alternative for vararg functions. For managed functions called only by managed clients, the managed alternative can have several advantages over C-style vararg functions. It is often easier to use than macros like va_start, va_arg, and va_end. In addition to that, this alternative is language interoperable; other .NET languages can seamlessly call a function like CallAnyFunction. And finally, this approach is typed. Instead of array<Object^>^, any one-dimensional managed array type can be used. The following code defines a function that can take an arbitrary number of int arguments: int Sum(... array<int>^ args) { int result = 0; for each (int i in args) result += i; return result; } To invoke such a function, only int values or values with a standard conversion to int can be passed.

retrieve the needed data. First, read the employee table to get all supervisor rows. Next, read the dept table to get all Dallas departments. Finally, join the rows you derived from the employee and the dept tables. The following would be the total cost of performing the query: Reading the employee table to get the supervisor rows: 2,000 reads Writing the supervisor rows derived in the previous step: 40 writes Reading the dept table to get all Dallas departments: 40 reads Writing the Dallas department rows derived from the previous step: 10 writes Joining the supervisor rows and department rows derived in the previous steps of this query execution: A total of 40 + 10 = 50 writes Reading the join result from the previous step: 50 reads Total I/O cost: 2,000 + 2(40) + 10 + 2(50) = 2,190 This example, simplified as it may be, shows you that Cartesian products are more expensive than more restrictive joins. Even a selective join operation, the results show, is more expensive than a selection operation. Although a join operation is in query 3, it s a join of two reduced relations; the size of the join is much smaller than the join in query 2. Query optimization often involves early selection (picking only some rows) and projection (picking only some columns) operations to reduce the size of the resulting outputs or row sources.