> I'm doing some maintanence in a application where I've found a lot of
> code like this:
>
> strSql = _
> "SELECT u.id_usr, u.cd_usr, p.nm_psoa, u.nr_niv_hier_usr" & _
> " FROM " & GlobalDB.TABLE_USERS & _
> " u, " & GlobalDB.TABLE_PERSONS & _
> " p WHERE u.fl_exc_usr = 0 AND p.id_psoa = u.id_psoa" & _
> " ORDER BY p.nm_psoa, u.nr_niv_hier_usr"
>
> I'd like to know if vb.net compiler is smart enough to detect this at
> compiler time and replace for a unique string resulting from the
> concatenation of all strings or  the concatenation will occur at run
> time?

> vcinqu***@gmail.com wrote:
>
> > strSql = _
> > "SELECT u.id_usr, u.cd_usr, p.nm_psoa, u.nr_niv_hier_usr" & _
> > " FROM " & GlobalDB.TABLE_USERS & _
> > " u, " & GlobalDB.TABLE_PERSONS & _
> > " p WHERE u.fl_exc_usr = 0 AND p.id_psoa = u.id_psoa" & _
> > " ORDER BY p.nm_psoa, u.nr_niv_hier_usr"
> >
> > I'd like to know if vb.net compiler is smart enough to detect this at
> > compiler time and replace for a unique string resulting from the
> > concatenation of all strings
>
> Yes.  Hacking the above about a little to get this ...
>
> Public Sub SC()
>     Const TABLE_USERS As String = "USERS"
>     Const TABLE_PERSONS As String = "PERSONS"
>     Dim s As String
>     s = _
>        "SELECT u.id_usr, u.cd_usr, p.nm_psoa, u.nr_niv_hier_usr" & _
>        " FROM " & TABLE_USERS & _
>        " u, " & TABLE_PERSONS & _
>        " p WHERE u.fl_exc_usr = 0 AND p.id_psoa = u.id_psoa" & _
>        " ORDER BY p.nm_psoa, u.nr_niv_hier_usr"
> End Sub
>
> ... building it and then pulling the resulting .exe apart again using
> ILDAsm, the I.L.Code created looks something like
>
> .method public instance void  SC() cil managed
> {
>    // Code size       9 (0x9)
>    .maxstack  1
>    .locals init ([0] string s)
>    IL_0000:  nop
>    IL_0001:  ldstr      "SELECT u.id_usr, u.cd_usr, p.nm_psoa, u.nr_niv_hie"
>    + "r_usr FROM USERS u, PERSONS p WHERE u.fl_exc_usr = 0 AND p.id_psoa
> = u."
>    + "id_psoa ORDER BY p.nm_psoa, u.nr_niv_hier_usr"
>    IL_0006:  stloc.0
>    IL_0007:  nop
>    IL_0008:  ret
> }
>
> Not a call to String.Concat in sight, so it's all done at compile time.
>
> HTH,
>     Phill  W.

> >Which one would have best performance?
>
> No difference. There's no concatenation being performed at runtime in
> either case. It's just the IL disassembler that breaks up the string
> for readability. Just like the VB compiler, the IL assembler can
> concatenate string constants at compile time.
>
> But even if there was a difference, it would be negligible compared to
> the actual database query. Don't waste your time on micro
> optimizations.
>
>
> Mattias
>
> --
> Mattias Sjögren [C# MVP]  mattias @ mvps.org
> http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
> Please reply only to the newsgroup.