TRUNC

Truncates a date or timestamp to a specified precision. This function follows a widely adopted date truncation syntax, making it easier for users migrating from other database systems.

Syntax

TRUNC(<date_or_timestamp>, <datetime_interval_type>)

Week Start Configuration

When using WEEK as the datetime interval type, the result depends on the week_start setting, which defines the first day of the week:

• week_start = 1 (default): Monday is considered the first day of the week
• week_start = 0: Sunday is considered the first day of the week

You can use the SETTINGS clause to change this setting for a specific query:

-- Set Sunday as the first day of the week
SETTINGS (week_start = 0) SELECT TRUNC(to_date('2024-04-05'), 'WEEK');

-- Set Monday as the first day of the week (default)
SETTINGS (week_start = 1) SELECT TRUNC(to_date('2024-04-05'), 'WEEK');

Return Type

Same as <date_or_timestamp>.

Examples

-- Truncate to different precisions
SELECT
    TRUNC(to_date('2022-07-07'), 'MONTH'),
    TRUNC(to_date('2022-07-07'), 'WEEK'),
    TRUNC(to_date('2022-07-07'), 'YEAR');

┌────────────────────────────────────────────────────────────────────────────────────┐
│ TRUNC(to_date('2022-07-07'), 'MONTH') │ TRUNC(to_date('2022-07-07'), 'WEEK') │ TRUNC(to_date('2022-07-07'), 'YEAR') │
├──────────────────────────────────────┼─────────────────────────────────────┼─────────────────────────────────────┤
│ 2022-07-01                           │ 2022-07-04                          │ 2022-01-01                          │
└────────────────────────────────────────────────────────────────────────────────────┘

The following example demonstrates how the week_start setting affects the result of TRUNC with WEEK precision:

-- Default: week_start = 1 (Monday as first day of week)
SELECT TRUNC(to_date('2024-04-03'), 'WEEK');  -- Wednesday

┌─────────────────────────────────────┐
│ TRUNC(to_date('2024-04-03'), 'WEEK') │
├─────────────────────────────────────┤
│ 2024-04-01                          │ -- Monday
└─────────────────────────────────────┘

-- Setting week_start = 0 (Sunday as first day of week)
SETTINGS (week_start = 0) SELECT TRUNC(to_date('2024-04-03'), 'WEEK');  -- Wednesday

┌─────────────────────────────────────┐
│ TRUNC(to_date('2024-04-03'), 'WEEK') │
├─────────────────────────────────────┤
│ 2024-03-31                          │ -- Sunday
└─────────────────────────────────────┘

Using TRUNC with timestamp values:

SELECT TRUNC(to_timestamp('2022-07-07 15:30:45.123456'), 'DAY');

┌───────────────────────────────────────────────────────┐
│ TRUNC(to_timestamp('2022-07-07 15:30:45.123456'), 'DAY') │
├───────────────────────────────────────────────────────┤
│ 2022-07-07 00:00:00.000000                            │
└───────────────────────────────────────────────────────┘