how to change date format in oracle session

Question

Accepted Answer

You can change the date format in an Oracle session using the `ALTER SESSION` command with the `NLS_DATE_FORMAT` parameter. This affects how dates are displayed and how they're interpreted when converted to strings.

The most common approach is:

```sql
ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD';
```

Replace `'YYYY-MM-DD'` with your desired format. Common format patterns include:
- `DD-MON-YYYY` (e.g., 15-JAN-2024)
- `MM/DD/YYYY` (e.g., 01/15/2024)
- `YYYY-MM-DD HH24:MI:SS` (includes time)
- `DD/MM/YYYY` (e.g., 15/01/2024)

This change applies only to your current session and is lost when you disconnect. To make it permanent, add the command to your login.sql file or set `NLS_DATE_FORMAT` in your environment variables.

Alternatively, use the `TO_CHAR()` function to format dates in specific queries without changing the session default:

```sql
SELECT TO_CHAR(hire_date, 'YYYY-MM-DD') FROM employees;
```

You can also view your current date format with:

```sql
SELECT * FROM NLS_SESSION_PARAMETERS WHERE PARAMETER = 'NLS_DATE_FORMAT';
```

Be aware that changing session formats can affect how date strings are implicitly converted, which may impact application behavior if dates are compared as strings rather than date types.