var1=123456
var2=RIGHT(ALLTRIM(STR(var1)),3)
var1=123456
var2=alltrim(str(substr(var1,1,3))) && Here You try to get first 3 symbols from var1 but substr wotks ONLY on string. You must change the sequence of the functions
var2=SUBSTR(ALLTRIM(STR(var1)),1,3)
Against Stupidity the Gods themselves Contend in Vain - Johann Christoph Friedrich von Schiller
The only thing normal about database guys is their tables.