DATE_TRUNC documentation is inconsistent with actual argument order behavior

[jodotlearn]

https://doris.apache.org/docs/3.x/sql-manual/sql-functions/scalar-functions/date-time-functions/date-trunc

The DATE_TRUNC documentation states that both argument orders are supported:

DATE_TRUNC(<datetime>, <time_unit>)
DATE_TRUNC(<time_unit>, <datetime>)

However, in actual usage, only the following argument order appears to work:

DATE_TRUNC(<datetime>, <time_unit>)

The reversed form:

DATE_TRUNC(<time_unit>, <datetime>)

results in an error.

Reproduction

Case 1: Using a DATETIME column

The datetime-first form works as expected:

SELECT DATE_TRUNC(work_date, 'month');

However, reversing the arguments:

SELECT DATE_TRUNC('month', work_date);

returns:

SQL Error [1105] [HY000]: errCode = 2, detailMessage =
the second parameter of date_trunc function must be a string constant:
date_trunc('month', work_date)

This suggests that the second argument is still interpreted as time_unit.

Case 2: Using only string literals

The same behavior can be reproduced without using a column:

SELECT DATE_TRUNC('month', '2010-12-02 19:28:30');

which returns:

SQL Error [1105] [HY000]: errCode = 2, detailMessage =
date_trunc function second param only support argument is
year|quarter|month|week|day|hour|minute|second

Again, this indicates that the second argument is interpreted as time_unit, rather than the first argument.

In contrast, the datetime-first form works:

SELECT DATE_TRUNC('2010-12-02 19:28:30', 'month');

Expected behavior

According to the documentation, both forms should be accepted:

DATE_TRUNC(work_date, 'month')
DATE_TRUNC('month', work_date)

Actual behavior

Only the datetime-first form appears to be supported:

DATE_TRUNC(<datetime>, <time_unit>)

Question

Could you please confirm whether:

1. DATE_TRUNC(<time_unit>, <datetime>) is intended to be supported; or

2. the documentation should only list:

   DATE_TRUNC(<datetime>, <time_unit>)

If the reversed argument order is only supported in specific Doris versions, it would also be helpful to clarify the supported versions in the documentation.

Environment

Apache Doris version: 3.0.4