ほぼタイトルママなんだけど SELECT DATE(created_at), COUNT(1) FROM users GROUP BY 1; ってクエリを見つけて、 GROUP BY 1 ってなんぞ……?という話。 MySQL のドキュメント には [GROUP BY {col_name | expr | position}, ... [WITH ROLLUP]] [ORDER BY {col_name | expr | position} Columns selected for output can be referred to in ORDER BY and GROUP BY clauses using column names, column aliases, or column positions. Column positions are integers and begin