How to truncate a value to a given decimal place using the TRUNCATE() function?

TRUNCATE(X, D) is a MySQL built-in function that truncates X to decimal place of D. For example:

SELECT TRUNCATE(-1.58, 0), TRUNCATE(23.298, 1), TRUNCATE(23.298, -1);
  -- +--------------------+---------------------+----------------------+
  -- | TRUNCATE(-1.58, 0) | TRUNCATE(23.298, 1) | TRUNCATE(23.298, -1) |
  -- +--------------------+---------------------+----------------------+
  -- |                 -1 |                23.2 |                   20 |
  -- +--------------------+---------------------+----------------------+

Reference information of the TRUNCATE() function:

TRUNCATE(X, D): val
  Returns the number X, truncated to D decimal places. If D is 0, the
  result has no decimal point or fractional part. D can be negative to
  cause D digits left of the decimal point of the value X to become
  zero.

Arguments, return value and availability:
  X: Required. The value to be truncated.
  D: Optional. Default is 0. The decimal place to truncate to.
  val: Return value. The truncated value.
  Available since MySQL 4.0.

Related MySQL functions:

• ROUND() - Rounding to Decimal Place

⇒ MySQL Functions on Date and Time

⇐ TAN() - Tangent Trigonometric Value

⇑ MySQL Functions on Numeric Values

⇑⇑ MySQL Function References