TRUNC Number FAQS

 1. What does the TRUNC function do in Oracle SQL?

The TRUNC function in Oracle is used to truncate a numeric or date value to a specified number of decimal places or to the left of the decimal point. It removes the fractional part of a number without rounding.

2. How do I use the TRUNC function in Oracle?

The basic syntax of the TRUNC function is:

TRUNC(number, decimal_places)

• number: The numeric value you want to truncate.
• decimal_places: The number of decimal places to truncate to. If this parameter is omitted, it defaults to 0, truncating the number to the nearest integer.

3. What happens if I omit the decimal_places parameter in TRUNC?

If you omit the decimal_places parameter, the TRUNC function truncates the number to 0 decimal places, effectively removing any digits after the decimal point.

Example:

SELECT TRUNC(123.4567) FROM dual;

-- Output: 123

4. Can I use TRUNC to truncate to the left of the decimal point?

Yes, by passing a negative value for decimal_places, the TRUNC function can truncate the number to the left of the decimal point (e.g., nearest ten, hundred, thousand, etc.).

Example:

SELECT TRUNC(12345, -2) FROM dual;

-- Output: 12300

5. How does TRUNC handle negative numbers?

The TRUNC function works with negative numbers in the same way it works with positive numbers, removing the fractional part or truncating to the left of the decimal point without rounding.

Example:

SELECT TRUNC(-123.4567, 2) FROM dual;

-- Output: -123.45

6. How is TRUNC different from ROUND?

• TRUNC: Simply removes the digits after the specified decimal place or truncates to the left of the decimal point without rounding.
• ROUND: Rounds the number to the nearest value based on standard rounding rules (e.g., numbers 5 or greater are rounded up).

Example:

SELECT ROUND(123.4567, 2) FROM dual;  -- Output: 123.46

SELECT TRUNC(123.4567, 2) FROM dual;  -- Output: 123.45

7. Can I truncate dates using the TRUNC function?

Yes, the TRUNC function can also be used to truncate date values to a specific unit like the day, month, or year.

• Truncate to the nearest day:

SELECT TRUNC(SYSDATE) FROM dual;

-- Output: Current date truncated to midnight (e.g., 27-FEB-2025 00:00:00)

• Truncate to the nearest month:

SELECT TRUNC(SYSDATE, 'MM') FROM dual;

-- Output: Current date truncated to the first day of the current month (e.g., 01-FEB-2025)

• Truncate to the nearest year:

SELECT TRUNC(SYSDATE, 'YYYY') FROM dual;

-- Output: Current date truncated to the first day of the current year (e.g., 01-JAN-2025)

8. What are the performance implications of using TRUNC?

The TRUNC function is quite efficient for small datasets. However, when used on large datasets, especially in JOIN operations or subqueries, it may impact performance. Using indexing on columns that are frequently truncated can help improve performance.

9. Can TRUNC be used in UPDATE statements?

Yes, you can use the TRUNC function in UPDATE statements to modify values in a table.

Example:

UPDATE products

SET price = TRUNC(price, 2)

WHERE product_id = 101;

10. What happens if I truncate a value to 0 decimal places?

When truncating a numeric value to 0 decimal places, it removes the decimal part and returns the integer part.

Example:

SELECT TRUNC(123.4567, 0) FROM dual;

-- Output: 123

11. How can I truncate a large number like 1234567 to the nearest thousand?

You can truncate large numbers to a specified unit (like thousands, hundreds, etc.) by providing a negative value for decimal_places.

Example:

SELECT TRUNC(1234567, -3) FROM dual;

-- Output: 1234000

12. Can I truncate a number to any specific decimal place?

Yes, you can truncate a number to any desired decimal place by specifying the number of decimal places in the TRUNC function.

Example:

SELECT TRUNC(123.456789, 4) FROM dual;

-- Output: 123.4567