This may sound stupid but...
When I create big SQL commands I want to keep my code readable and I do this:
cmd.CommandText = "SELECT top 10 UserID, UserName " +
"FROM Users " +
"INNER JOIN SomeOtherTable ON xxxxx " +
"WHERE UserID IN (blablabla)";
See the concatenations? Now, to save performance I now do this:
cmd.CommandText = @"SELECT top 10 UserID, UserName
FROM Users
INNER JOIN SomeOtherTable ON xxxxx
WHERE UserID IN (blablabla)";
It keeps the code readable but saves concatenations. Now does it really save any performance or the compiler is smart enough to "pre-concatenate" the first string?
C is saying that if the word C is found in context later in the SQL it is a reference to the table named productos . It is an alias for the table named immediately before the first occurance of C in your SQL query. Looks like simple alias for table products.
To undestand the difference between a language like C and SQL is that basically SQL is a specialized type of language that is concerned with database operations. C is less concerned with accessing the data than with how the whole application will work.
Yes the compiler is smart enough to optimize constant string concatenations. To prove this let's examine the following method:
public static string Concat()
{
return "a" + "b";
}
Compiled in Release mode this produces the following IL:
.method public hidebysig static string Concat() cil managed
{
.maxstack 8
L_0000: ldstr "ab"
L_0005: ret
}
Notice the optimization. So in terms of performance both methods are identical. The only difference is that in the second case you will get new lines (\r\n) in the string, so they won't produce the exactly same string but SQL Server is also smart enough :-)
Yes, the compiler will compute arithemetical operations on constant numbers and strings at compile time. However, the better way to answer performance questions like this is to try it yourself. Get out the StopWatch class, write the code both ways, run it a billion times in a loop, and then you'll know.
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