docs/sql-manual/sql-functions/debug-functions/nullable.md

---
{
    "title": "NULLABLE",
    "language": "en"
}
---

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## nullable
### description

:::tip
For developer debugging only, do not call this function manually in the production environment.
:::

#### Syntax

`T nullable(T expr)`

Converts `expr` to nullable, or to itself if `expr` is already nullable.

### example

```sql
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