Function table / Dates / DATETRUNC

DATETRUNC: from Tableau to SQL

Truncates a date to a date-part boundary. Below, 8 sample rows go through the calculation and through the SQL, and both return the same numbers.

Calculated field

DATETRUNC('week',[shipped],'sunday')

Sample data

shipmentshippedreceivedtextyearmonthdayhourminutesecondlatlonwkt
12024-12-292024-12-29T16:25:402024-12-2920252259254010106POINT (106 10)
22024-12-302024-12-30T16:25:402024-12-30202522610254010.1106.1POINT (106.1 10.1)
32025-01-012025-01-01T16:25:402025-01-01202522711254010.2106.2POINT (106.2 10.2)
42025-01-312025-01-31T16:25:402025-01-31202522812254010.3106.3POINT (106.3 10.3)
52025-02-282025-02-28T16:25:402025-02-28202522913254010.4106.4POINT (106.4 10.4)
62025-03-152025-03-15T16:25:402025-03-15202523014254010.5106.5POINT (106.5 10.5)
7nullnullnull202523115254010.6106.6POINT (106.6 10.6)
82024-02-292024-02-29T16:25:402024-02-29202523216254010.7106.7POINT (106.7 10.7)

The same calculation as SQL

SELECT CAST(date_trunc('week',shipped+INTERVAL '1 day')-INTERVAL '1 day' AS DATE) AS result FROM input ORDER BY shipment

Runs the example above.

Result

shipmentshippedreceivedtextresult
12024-12-292024-12-29T16:25:402024-12-292024-12-29
22024-12-302024-12-30T16:25:402024-12-302024-12-29
32025-01-012025-01-01T16:25:402025-01-012024-12-29
42025-01-312025-01-31T16:25:402025-01-312025-01-26
52025-02-282025-02-28T16:25:402025-02-282025-02-23
62025-03-152025-03-15T16:25:402025-03-152025-03-09
7nullnullnullnull
82024-02-292024-02-29T16:25:402024-02-292024-02-25

Same rows from the calculation and from the SQL in DuckDB.

Where a naive translation goes wrong

  • The week start changes the truncated date.

    Naive SQL

    SELECT CAST(date_trunc('week',shipped) AS DATE) AS result FROM input ORDER BY shipment
    shipmentshippedreceivedtextresult
    12024-12-292024-12-29T16:25:402024-12-292024-12-23
    22024-12-302024-12-30T16:25:402024-12-302024-12-30
    32025-01-012025-01-01T16:25:402025-01-012024-12-30
    42025-01-312025-01-31T16:25:402025-01-312025-01-27
    52025-02-282025-02-28T16:25:402025-02-282025-02-24
    62025-03-152025-03-15T16:25:402025-03-152025-03-10
    7nullnullnullnull
    82024-02-292024-02-29T16:25:402024-02-292024-02-26

    Matches the calculation

    SELECT CAST(date_trunc('week',shipped+INTERVAL '1 day')-INTERVAL '1 day' AS DATE) AS result FROM input ORDER BY shipment
    shipmentshippedreceivedtextresult
    12024-12-292024-12-29T16:25:402024-12-292024-12-29
    22024-12-302024-12-30T16:25:402024-12-302024-12-29
    32025-01-012025-01-01T16:25:402025-01-012024-12-29
    42025-01-312025-01-31T16:25:402025-01-312025-01-26
    52025-02-282025-02-28T16:25:402025-02-282025-02-23
    62025-03-152025-03-15T16:25:402025-03-152025-03-09
    7nullnullnullnull
    82024-02-292024-02-29T16:25:402024-02-292024-02-25

Signature

DATETRUNC(date_part, date, [start_of_week])