如何在不引用任何表的情况下使用 SELECT 来计算 MySQL 中的表达式？

SELECT expression;

mysql> Select 10 DIV 5;
+----------+
| 10 DIV 5 |
+----------+
|        2 |
+----------+
1 row in set (0.06 sec)

mysql> Select 10*5;
+------+
| 10*5 |
+------+
|   50 |
+------+
1 row in set (0.00 sec)

mysql> Set @var1 = 100, @var2 = 200;
Query OK, 0 rows affected (0.00 sec)

mysql> Select @Var1+@Var2;
+-------------+
| @Var1+@Var2 |
+-------------+
|         300 |
+-------------+
1 row in set (0.00 sec)