In MySQL, when I executed SQL that looked absolutely fine, a syntax error occurred.

ERROR 1064 (42000): You have an error in your SQL syntax;

mysql> SELECT * FROM addresses ORDER BY primary;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'primary' at line 1

primary is a reserved word

Since primary is apparently a reserved word, it was fine when I surrounded it with single quotes and executed it.

mysql> SELECT * FROM addresses ORDER BY 'primary';

参考情報

• MySQL :: MySQL 5.1 リファレンスマニュアル :: 8.3 MySQLでの予約語の扱い

That’s all from the Gemba.