Straight quotes can be used like backticks around aliases IN SOME CASES (as of 5.0.15, at least). Observe:
CREATE TABLE myTable (id int, someData int);
INSERT INTO myTable VALUES (1, 1), (1, 2), (1, 3), (2, 1), (2, 2);
These three queries produce identical output:
SELECT * FROM myTable GROUP BY id;
SELECT * FROM myTable GROUP BY `id`;
SELECT * FROM myTable GROUP BY 'id';
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