support DATETRUNC() function

[skumawat2025]

Description

With this pull request babelfish now supports function DATETRUNC().

The DATETRUNC function returns an input date truncated to a specified datepart.

For the implementation of the 'DATETRUNC' function, the PostgreSQL 'date_trunc' function was utilized with certain custom modifications to meet specific requirements.

Example -

SELECT DATETRUNC(year, CAST('2021-12-08 11:30:15.1234567' as datetime2))
2021-01-01 00:00:00.0000000

SELECT DATETRUNC(month, '1998-03-04');
1998-03-01 00:00:00.0000000

For detailed explanation -
Reference - https://github.com/MicrosoftDocs/sql-docs/blob/live/docs/t-sql/functions/datetrunc-transact-sql.md

Limitation

There are some limitation of current implementation of DATETRUNC() function, when a specific scale provided during casting to time, datetime2, datetimeoffset datatypes.

1. The output should match the fractional time scale same as the input data type. But currently BBF output will always be till 7 fractional digits not matter what is input data type fractional time-scale.

Example.

SELECT DATETRUNC(MILLISECOND, CAST('09:23:32.23456' as time(4)));
EXPECTED:- 09:23:32.2340
BBF:- 09:23:32.2340000

SELECT DATETRUNC(Month, CAST('2012-02-02 09:23:32.23456' as datetime2(1)));
EXPECTED:- 2012-02-01 00:00:00.0
BBF:- 2012-02-01 00:00:00.0000000

2. When the fractional time-scale of input data type is not sufficient for provided datepart, function DATETRUNC should throw an error message, but currently BBF's definition of DATETRUNC will give output by assuming required fractional seconds digits as 0.

Example.

SELECT DATETRUNC(MILLISECOND, CAST('2012-02-02 09:23:32.23456' as datetime2(2)));
EXPECTED:- The datepart millisecond is not supported by date function datetrunc for data type datetime2
BBF:-2012-02-02 09:23:32.2300000

SELECT DATETRUNC(MILLISECOND, CAST('2012-02-02 09:23:32.23456 +02:12' as datetimeoffset(2)));
EXPECTED:- The datepart millisecond is not supported by date function datetrunc for data type datetimeoffset
BBF:- 2012-02-02 09:23:32.2300000 +02:12

Signed-off-by: Sandeep Kumawat [email protected]

Issues Resolved

BABEL-3953

Test Scenarios Covered

• Use case based - Added

• Boundary conditions - Added

• Arbitrary inputs - Added

• Negative test cases - Added

• Minor version upgrade tests- Added

• Major version upgrade tests - Added

• Performance tests - NA

• Tooling impact - NA

• Client tests - NA

Check List

• Commits are signed per the DCO using --signoff

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[hash-16]

You can add limitation of this function in PR description with some examples.

[hash-16]

Please resolve the merge conflicts.

[hash-16]

Lets add all testcases from the doc and verify it against standard TSQL.

[jsudrik]

Approved.

[jsudrik]

With this change, babelfish now supports function DATETRUNC().

The DATETRUNC function returns an input date truncated to a specified datepart.