Column 'mary' does not exist

i'm doing a simple query here and it returns that column 'Mary' does not exist:

SELECT  telephone.telephonenumber as tel
FROM    person, telephone
WHERE   person.idperson = telephone.idperson
AND person.personname = ‘Mary’;

Can someone explain what can be happening? I don't want Mary as a column, but as a value.

Thanks in advance, Gabriel

Use plain single quotes to delimit a string literal 'Mary' not smart quotes ‘Mary’

Make sure that you are quoting your string correctly.

From your snippet, I'd say that's the problem here since you're using something else than simple single quotes.