SELECT / WHERE and Global Variable

Hello,

[AUTHOR] is a global variable and contains the string ‘Shakespeare’.

In a grid, I have a Selection box with the automatic query :

SELECT book_id, book_title
FROM books
WHERE author = ‘Shakespeare’

This woks fine. But with the global variable [AUTHOR] it crashes :

SELECT book_id, book_title
FROM books
WHERE author = ‘[AUTHOR]’

Has anyone an idea ?
Sincerely
SC 9.0.034