Categories:

Numeric Functions (Rounding and Truncation)

ROUND

Returns rounded values for input_expr.

See also:

CEIL , FLOOR , TRUNCATE , TRUNC

Syntax

ROUND( <input_expr> [ , <scale_expr> [ , <rounding_mode> ] ] )
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ROUND( EXPR => <input_expr> ,
       SCALE => <scale_expr>
       [ , ROUNDING_MODE => <rounding_mode>  ] )
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Arguments

Required:

input_expr . OR . EXPR => input_expr

The value or expression to operate on. The data type should be one of the numeric data types, such as FLOAT or NUMBER.

If you specify the EXPR => named argument, you must also specify the SCALE => named argument.

Optional:

scale_expr . OR . SCALE => scale_expr

The number of digits the output should include after the decimal point. The expression should evaluate to an integer from -38 to +38.

The default scale_expr is zero, meaning that the function removes all digits after the decimal point.

For information about negative numbers, see the Usage Notes below.

If you specify the SCALE => named argument, you must specify EXPR => as the preceding named argument.

rounding_mode . OR . ROUNDING_MODE => rounding_mode

The rounding mode to use. You can specify one of the following values:

Default: 'HALF_AWAY_FROM_ZERO'

If you specify the ROUNDING_MODE => named argument, you must specify both EXPR => and SCALE => as preceding named arguments.

Note

If you specify either value for the rounding_mode argument, the data type of input_expr must be one of the data types for a fixed-point number.

Data types for floating point numbers (e.g. FLOAT) are not supported with this argument.

Returns

The return type is based on the input type:

  • If the input is FLOAT, the data type of the returned value is FLOAT.

  • If the input is NUMBER, the data type of the returned value is NUMBER.

    If the input scale is greater than or equal to zero, the output scale generally matches the input scale.

    If the input scale is negative, the output scale is 0.

    For example:

    • The data type returned by ROUND(3.14::NUMBER(4, 1), 1) is NUMBER(4, 1).

    • The data type returned by ROUND(3.14::NUMBER(4, 0), 0) is NUMBER(4, 0).

If the scale is zero, the value is effectively an integer.

Usage Notes

  • You must either specify all arguments by name or by position. You cannot specify some of the arguments by name and other arguments by position.

    When specifying an argument by name, you cannot use double quotes around the argument name.

  • If scale_expr is negative, it specifies the number of places before the decimal point to which to adjust the number. For example, if the scale is -2, the result is a multiple of 100.

  • If scale_expr is larger than the input expression scale, the function does not have any effect.

  • If either the input_expr or the scale_expr is NULL, the result is NULL.

  • By default, half-points are rounded away from zero for decimals. For example, -0.5 is rounded to -1.0.

    To change the rounding mode to round the value half to even (e.g. to round -0.5 to 0), pass in 'HALF_TO_EVEN' for the rounding_mode argument.

    Note

    If you specify the rounding_mode argument, the data type of the input_expr argument must be one of the data types for a fixed-point number.

  • Floating point numbers are approximate values. A floating point number might not round as expected.

  • If rounding brings the number outside of the range of values of the data type, the function returns an error.

Examples

This first example shows a simple use of ROUND, with the default number of decimal places (0):

SELECT ROUND(135.135), ROUND(-975.975);
+----------------+-----------------+
| ROUND(135.135) | ROUND(-975.975) |
|----------------+-----------------|
|            135 |            -976 |
+----------------+-----------------+
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The next example uses a range of values for the scale parameter:

SELECT n, scale, ROUND(n, scale)
  FROM test_ceiling
  ORDER BY n, scale;
+----------+-------+-----------------+
|        N | SCALE | ROUND(N, SCALE) |
|----------+-------+-----------------|
| -975.975 |    -1 |        -980     |
| -975.975 |     0 |        -976     |
| -975.975 |     2 |        -975.98  |
|  135.135 |    -2 |         100     |
|  135.135 |     0 |         135     |
|  135.135 |     1 |         135.1   |
|  135.135 |     3 |         135.135 |
|  135.135 |    50 |         135.135 |
|  135.135 |  NULL |            NULL |
+----------+-------+-----------------+
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The next two examples show the difference between using the default rounding mode ('HALF_AWAY_FROM_ZERO') and the rounding mode 'HALF_TO_EVEN'. Both examples call the ROUND function twice, first with the default rounding behavior, then with 'HALF_TO_EVEN'.

The first example uses a positive input value of 2.5:

SELECT ROUND(2.5, 0), ROUND(2.5, 0, 'HALF_TO_EVEN');
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+---------------+-------------------------------+
| ROUND(2.5, 0) | ROUND(2.5, 0, 'HALF_TO_EVEN') |
|---------------+-------------------------------|
|             3 |                             2 |
+---------------+-------------------------------+

The second example uses a negative input value of -2.5:

SELECT ROUND(-2.5, 0), ROUND(2.5, 0, 'HALF_TO_EVEN');
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+---------------+--------------------------------+
| ROUND(2.5, 0) | ROUND(-2.5, 0, 'HALF_TO_EVEN') |
|---------------+--------------------------------|
|            -3 |                             -2 |
+---------------+--------------------------------+

The next two examples demonstrate how to specify the arguments to the function by name, rather than by position.

SELECT ROUND(
  EXPR => -2.5,
  SCALE => 0);
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+---------------------------------+
| ROUND(EXPR => -2.5, SCALE => 0) |
|---------------------------------|
|                              -3 |
+---------------------------------+
SELECT ROUND(
  EXPR => -2.5,
  SCALE => 0,
  ROUNDING_MODE => 'HALF_TO_EVEN');
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+------------------------------------------------------------------+
| ROUND(EXPR => -2.5, SCALE => 0, ROUNDING_MODE => 'HALF_TO_EVEN') |
|------------------------------------------------------------------|
|                                                               -2 |
+------------------------------------------------------------------+

The next example shows that FLOAT values are not always stored exactly. As you can see below, in some cases .005 is rounded to .01, while in other cases it is rounded to 0. The difference is not in the rounding; the difference is actually in the underlying representation of the floating point number; 1.005 is stored as a number very slightly smaller than 1.005 (approximately 1.004999). The DECIMAL value, however is stored as an exact number, and is rounded to .01 as expected in all cases.

Create and load a table:

CREATE OR REPLACE TEMP TABLE rnd1(f float, d DECIMAL(10, 3));
INSERT INTO rnd1 (f, d) VALUES
      ( -10.005,  -10.005),
      (  -1.005,   -1.005),
      (   1.005,    1.005),
      (  10.005,   10.005)
      ;
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Show examples of the difference between rounded FLOAT values and rounded DECIMAL values:

select f, round(f, 2), 
       d, round(d, 2) 
    from rnd1 
    order by 1;
+---------+-------------+---------+-------------+
|       F | ROUND(F, 2) |       D | ROUND(D, 2) |
|---------+-------------+---------+-------------|
| -10.005 |      -10.01 | -10.005 |      -10.01 |
|  -1.005 |       -1    |  -1.005 |       -1.01 |
|   1.005 |        1    |   1.005 |        1.01 |
|  10.005 |       10.01 |  10.005 |       10.01 |
+---------+-------------+---------+-------------+
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