### E

### Function Description
The e() function is used to return the base of the natural logarithm, which is the mathematical constant e.

### Syntax
```
e()
```
### Return Type
The return value type is double.

### Usage Example
The following is an example of using the e() function:
```sql
-- Query the value of e
SELECT e();
```
After executing the above query, the value of the natural constant e will be returned, which is approximately 2.7182818284590451.

### Example and Explanation
1. Query the value of e alone:
   ```sql
   SELECT e();
   ```
The result is as follows:
   ```
   2.7182818284590451
   ```