Creating temporary view from a temporary table in SQL Server
You can use a Common Table expression to do that: WITH Top10Records AS ( select top 10 * from #MytempTable ) SELECT * FROM Top10Records GO
temporary
Returning a c++ std::vector without a copy?
If your compiler supports the NRVO then no copy will be made, provided certain conditions are met in the function returning the object. Thankfully, this was finally added in Visual C++ 2005 (v8.0) This can have a major +ve impact on perf if the container is large, obviously. If your own compiler docs do not … Read more
Why is it legal to borrow a temporary?
Why is it legal to borrow a temporary? It’s legal for the same reason it’s illegal in C++ — because someone said that’s how it should be. How long does the temporary live in Rust? And since x is only a borrow, who is the owner of the string? The reference says: the temporary scope … Read more
Why lifetime of temporary doesn’t extend till lifetime of enclosing object?
The standard considers two circumstances under which the lifetime of a temporary is extended: §12.2/4 There are two contexts in which temporaries are destroyed at a different point than the end of the fullexpression. The first context is when an expression appears as an initializer for a declarator defining an object. In that context, the … Read more
C++ – using const reference to prolong a member of a temporary, ok or UB?
Your code should be well-formed, because for temporaries (emphasis mine) Whenever a reference is bound to a temporary or to a subobject thereof, the lifetime of the temporary is extended to match the lifetime of the reference Given A().b[4], b[4] is the subobject of b and the data member b is the subobject of the … Read more
Lifetime of temporaries
A temporary object is destroyed when the full-expression that lexically contains the rvalue whose evaluation created that temporary object is completely evaluated. Let me demonstrate with ASCII art: ____________________ full-expression ranges from ‘b’ to last ‘)’ bar( foo().c_str() ); ^^^^^ ^ | | birth funeral
MySQL: Auto increment temporary column in select statement
This will give you a consecutive row number with 3. SELECT (@cnt := @cnt + 1) AS rowNumber, t.rowID FROM myTable AS t CROSS JOIN (SELECT @cnt := 0) AS dummy WHERE t.CategoryID = 1 ORDER BY t.rowID ; Result | ROWNUMBER | ROWID | ——————— | 1 | 1 | | 2 | 25 … Read more
Address of a temporary in Go?
The address operator returns a pointer to something having a “home”, e.g. a variable. The value of the expression in your code is “homeless”. if you really need a *string, you’ll have to do it in 2 steps: tmp := a(); b := &tmp Note that while there are completely valid use cases for *string, … Read more
Using index, using temporary, using filesort – how to fix this?
Well, the doc gives the exact reasons when “Using temporary” will appear: Temporary tables can be created under conditions such as these: If there is an ORDER BY clause and a different GROUP BY clause, or if the ORDER BY or GROUP BY contains columns from tables other than the first table in the join … Read more
Do temp variables slow down my program?
A modern optimizing compiler should optimize those variables away, for example if we use the following example in godbolt with gcc using the -std=c99 -O3 flags (see it live): #include <stdio.h> void func() { int i = 5; int j = 10; int result = i + j; printf( “%d\n”, result ) ; } it … Read more