sql query with fieldName as variable name

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Hi Ruslan,
I will keep the fieldname as global variable name, how can I write it?

global fieldName
query = "SELECT RecID, * from STUDENTS WHERE fieldName = '" & searchString &
"'"

I've tried with:
query = "SELECT RecID, * from STUDENTS WHERE 'fieldName' = '" & searchString
& "'" and other forms
but I don't try the right way...

P.S. Thank Peter for the "nil" answer :-)