MySQL中的枚举值如何在表达式中使用？

众所周知，枚举值与索引值相关联，因此如果我们在表达式中使用枚举值，那么所有计算都将在索引号上完成。下面的例子将阐明它 -

mysql> Select * from Result;
+-----+--------+-------+
| Id  | Name   | Grade |
+-----+--------+-------+
| 100 | Gaurav | GOOD  |
| 101 | Rahul  | POOR  |
| 102 | Rahul  | NULL  |
| 103 | Mohan  |       |
+-----+--------+-------+
4 rows in set (0.00 sec)

mysql> Select SUM(Grade) from result;
+------------+
| SUM(Grade) |
+------------+
|          3 |
+------------+
1 row in set (0.00 sec)

mysql> Select AVG(Grade) from result;
+------------+
| AVG(Grade) |
+------------+
|          1 |
+------------+
1 row in set (0.00 sec)

mysql> Select Grade+0 from result;
+---------+
| Grade+0 |
+---------+
|       2 |
|       1 |
|    NULL |
|       0 |
+---------+
4 rows in set (0.00 sec)

mysql> Select Grade-1 from result;
+---------+
| Grade-1 |
+---------+
|       1 |
|       0 |
|    NULL |
|      -1 |
+---------+
4 rows in set (0.00 sec)

以上查询的结果显示了如何在表达式中使用枚举值。

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