NULLABLE
nullable
description
提示
仅供开发者调试用,请勿在生产环境手动调用该函数。
Syntax
T nullable(T expr)
转换 expr
为 nullable 属性,若 expr
已经是 nullable 的,则为其本身。
example
mysql> select k1, nullable(k1), nullable(1) from test_nullable_functions order by k1;
+------+--------------+-------------+
| k1 | nullable(k1) | nullable(1) |
+------+--------------+-------------+
| NULL | NULL | 1 |
| 1 | 1 | 1 |
| 2 | 2 | 1 |
| 3 | 3 | 1 |
| 4 | 4 | 1 |
+------+--------------+-------------+
keywords
nullable