A Big Bug: date type timezone bug

[p369349074]

Bug description

i am in my local, my date data save in my postgre,
just date type field;
but when i use this field in superset, you will make my date field to calculation by timezone,
so i think date type field can't calculate,
datetime field can calculate
this question hope you can fixed it soon
thanks.

Screenshots/recordings

No response

Superset version

master / latest-dev

Python version

3.11

Node version

16

Browser

Chrome

Additional context

No response

Checklist

• I have searched Superset docs and Slack and didn't find a solution to my problem.
• I have searched the GitHub issue tracker and didn't find a similar bug report.
• I have checked Superset's logs for errors and if I found a relevant Python stacktrace, I included it here as text in the "additional context" section.

[dosubot]

Hi @p369349074! I'm Dosu and I'm helping the Apache Superset team.

This happens because Superset applies PostgreSQL's DATE_TRUNC function to all temporal columns — including pure DATE fields — and DATE_TRUNC returns a TIMESTAMP WITH TIME ZONE, which triggers timezone conversion [1]. The get_timestamp_expr function does not differentiate between DATE and DATETIME/TIMESTAMP column types when generating time grain expressions [2]. Additionally, the dataset "HOURS OFFSET" setting is applied to all temporal columns in post-processing, including DATE fields [3].

Workarounds you can try:

1. Use a custom SQL expression in your dataset that casts back to DATE:

   DATE_TRUNC('day', your_date_column)::DATE

2. Check your dataset's HOURS OFFSET — make sure it's set to 0 (or unset) if you have DATE columns being affected.

3. Avoid applying time grains (day, month, year grouping) directly on DATE columns where possible, since that's what triggers DATE_TRUNC.

This does appear to be a gap in how Superset handles DATE vs DATETIME types — the codebase already distinguishes between them for literal date conversion [4], but that distinction isn't carried through to time grain expression generation.

To reply, just mention @dosu.

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[AmoghAtreya]

@dosu can I work on this?

[rusackas]

@AmoghAtreya go for it! No permission from 3rd party bots (or anyone) needed to open a PR :D