Batch file loosing variables in FOR loop - batch-file

Question

I am struggling with this one for some time now. Tried WITH and WITHOUT EnableDelayedExpansion, but no joy. Simply, the variable %MYFILENAME% is empty right after it's set in a loop:
::echo off
setlocal enabledelayedexpansion
echo -- BACKUP DATABASES --
set MYPATH=D:\SQL_BACKUP
set MYDBASES=db1 db2 db3 db4
For /f "tokens=2-4 delims=/ " %%a in ('date /t') do (set MYDATE=%%c%%a%%b)
For /f "tokens=1-2 delims=/:" %%a in ("%TIME%") do (set MYTIME=%%a-%%b)
set MYDATE=%MYDATE:.=-%
for %%q in (%MYDBASES%) do (
echo DB %%q processing
set MYFILENAME=%MYPATH%\%%q_%MYDATE%_%MYTIME%.bak
set SERVERNAME=.
echo %MYFILENAME%
echo sqlcmd -B -E -S %SERVERNAME% -d master -Q "BACKUP DATABASE [%%q] TO DISK = N'%MYFILENAME%' WITH INIT , NOUNLOAD , NAME = N'%%q backup', NOSKIP , STATS = 10, NOFORMAT"
if %ERRORLEVEL% == 0 (
echo OK
) else if %ERRORLEVEL% == 1 (
echo failed!
)
)
echo.
set MYDATE=
set MYTIME=
set BACKUPFILENAME=
set MYPATH=
set MYDBASES=
set MYFILENAME=
What I get is lost %MYFILENAME% imediatelly:
echo DB db1 processing
set MYFILENAME=db1_11-11-2016_0-54.bak
set SERVERNAME=.
echo <<<----------HERE MISSING MYFILENAME ----------<<<
echo sqlcmd -B -E -S . -d master -Q "BACKUP DATABASE [zdvrhnika] TO DISK = N''
WITH INIT , NOUNLOAD , NAME = N'zdvrhnika backup', NOSKIP , STATS = 10, NOFORMAT
"
Any idea?
EDIT
After changing MYFILENAME and SERVERNAME variables to some simple texts, I found out, that they do not change at all! MYFILENAME is always empty, and SERVERNAME is always ".", regardless of what I set them to?! And regardless of whether I use SETLOCAL EnableDelayedExpansion or not.
It's not script fault, but some environment stuff.

Answer 1

Within a block statement (a parenthesised series of statements), the entire block is parsed and then executed. Any %var% within the block will be replaced by that variable's value at the time the block is parsed - before the block is executed - the same thing applies to a FOR ... DO (block).
Hence, IF (something) else (somethingelse) will be executed using the values of %variables% at the time the IF is encountered.
Two common ways to overcome this are 1) to use setlocal enabledelayedexpansion **and use !var! in place of %var% to access the changed value of var ** or 2) to call a subroutine to perform further processing using the changed values.