TRUNC

Sample data

create table if not exists mf_math_fun_t(
    int_data     int,
    bigint_data  bigint,
    double_data  double,
    decimal_data decimal,
    float_data   float,
    string_data  string
);

insert into mf_math_fun_t values
(null, -10, 0.525, 0.525BD, cast(0.525 as float), '10'),
(-20, null, -0.1, -0.1BD, cast(-0.1 as float), '-10'),
(0, -1, null, 20.45BD, cast(-1 as float), '30'),
(-40, 4, 0.89, null, cast(0.89 as float), '-30'),
(5, -50, -1, -1BD, null, '50'),
(-60, 6, 1.5, 1.5BD, cast(1.5 as float), '-50'),
(-1, -70, -7.5, -7.5BD, cast(-7.5 as float), null),
(-80, 1, -10.2, -10.2BD, cast(-10.2 as float), '-1'),
(9, -90, 2.58, 2.58BD, cast(2.58 as float), '0'),
(-100, 10, -5.8, -5.8BD, cast(-5.8 as float), '-90');

Query the table:

select * from mf_math_fun_t;

Result:

+------------+-------------+-------------+--------------+------------+-------------+
| int_data   | bigint_data | double_data | decimal_data | float_data | string_data |
+------------+-------------+-------------+--------------+------------+-------------+
| NULL       | -10         | 0.525       | 0.525        | 0.525      | 10          |
| -20        | NULL        | -0.1        | -0.1         | -0.1       | -10         |
| 0          | -1          | NULL        | 20.45        | -1.0       | 30          |
| -40        | 4           | 0.89        | NULL         | 0.89       | -30         |
| 5          | -50         | -1.0        | -1           | NULL       | 50          |
| -60        | 6           | 1.5         | 1.5          | 1.5        | -50         |
| -1         | -70         | -7.5        | -7.5         | -7.5       | NULL        |
| -80        | 1           | -10.2       | -10.2        | -10.2      | -1          |
| 9          | -90         | 2.58        | 2.58         | 2.58       | 0           |
| -100       | 10          | -5.8        | -5.8         | -5.8       | -90         |
+------------+-------------+-------------+--------------+------------+-------------+

Example 1: Default behavior (no scale specified)

When decimal_places is omitted, TRUNC removes all decimal digits, returning the integer part closest to zero.

-- Returns 125.0
select trunc(125.815, 0);

Example 2: Positive scale

A positive decimal_places value keeps that many decimal digits. All examples below use 125.815 as the input.

-- Returns 125.80000000000001 (floating-point representation of 125.8)
select trunc(125.815, 1);
-- Returns 125.81
select trunc(125.815, 2);
-- Returns 125.815
select trunc(125.815, 3);
-- Returns 123.345 (scale exceeds available decimal digits; value is unchanged)
select trunc(123.345, 4);

Example 3: Negative scale

A negative decimal_places value truncates to the left of the decimal point. All examples below use 125.815 as the input.

-- Returns 120.0 (truncated to the tens place)
select trunc(125.815, -1);
-- Returns 100.0 (truncated to the hundreds place)
select trunc(125.815, -2);
-- Returns 0.0 (scale exceeds the integer part length)
select trunc(125.815, -3);
-- Returns 0.0 (scale exceeds the integer part length)
select trunc(123.345, -4);

Example 4: Negative input values

Truncation is towards zero. Compare trunc(-125.815, 2) with trunc(125.815, 2):

-- Returns -125.81 (towards zero, not towards -125.82)
select trunc(-125.815, 2);

Example 5: Null handling

If either argument is null, TRUNC returns null.

-- Returns null
select trunc(123.345, null);

Example 6: Table data

Truncate values in each column of the sample table to one decimal place.

select trunc(bigint_data, 1) as bigint_new,
       trunc(double_data, 1) as double_new,
       trunc(decimal_data, 1) as decimal_new,
       trunc(string_data, 1) as string_new
from mf_math_fun_t;

Result:

+------------+---------------------+-------------+------------+
| bigint_new | double_new          | decimal_new | string_new |
+------------+---------------------+-------------+------------+
| -10.0      | 0.5                 | 0.5         | 10.0       |
| NULL       | -0.1                | -0.1        | -10.0      |
| -1.0       | NULL                | 20.4        | 30.0       |
| 4.0        | 0.8                 | NULL        | -30.0      |
| -50.0      | -1.0                | -1          | 50.0       |
| 6.0        | 1.5                 | 1.5         | -50.0      |
| -70.0      | -7.5                | -7.5        | NULL       |
| 1.0        | -10.200000000000001 | -10.2       | -1.0       |
| -90.0      | 2.5                 | 2.5         | 0.0        |
| 10.0       | -5.800000000000001  | -5.8        | -90.0      |
+------------+---------------------+-------------+------------+