Support empty string handling for date and time datatypes

[manisha-deshpande]

Overview

Add TSQL-compatible handling of empty string ('') for date and time types, defaulting to '1900-01-01' for date and time, similar to datetime, datetime2, datetimeoffset, smalldatetime.

Task: BABEL-3433

Description

In SQL Server, when an empty string ('') is cast to date or time datatype, it should be return a default value - '1900-01-01' for date and '00:00:00.0000000' for time. Currently, Babelfish raises a syntax error for these cases. This change improves TSQL compatibility by matching SQL Server's behavior for empty string handling in date and time datatypes, while maintaining existing behavior for non-empty inputs.

1> create table bug(dt date null, tm time(3) null);
2> insert into bug values ('', '');
go
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
invalid input syntax for type date: ""
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
invalid input syntax for type time: ""

Changes:

1. • Added helper functions in babelfish_common's datetime.c for default value initialization:

• initializeToDefaultDate() - Returns default date '1900-01-01'
• initializeToDefaultTime() - Returns default time '00:00:00.0000000'
• isEmptyOrWhitespace() - Checks if string is empty or contains only whitespace

2. Modifying string to date/time conversion in two places:

• varchar2date() and varchar2time() functions for CAST operations from varchar and nvarchar types
• tsql_coerce_string_literal_hook for string literals

3. Added comprehensive test coverage in the Babelfish JDBC test suite to verify empty string handling across different scenarios including direct casts, table insert operation, type conversions, and formatting functions.

Remaining items out of current scope:

BABEL-5923

• Support for casts from char and nchar types to date and time datatypes. (Currently only supports varchar, nvarchar)
• Extend whitespace handling for other datetime types.
• Support tab space handling for all date time datatypes.

Issues Resolved

BABEL-3433: Support for empty input string handling in date and time datatypes

Test Scenarios Covered [+ BABEL_3433.sql]

• Use case based -

CREATE TABLE date_testing(d DATE);
INSERT INTO date_testing VALUES('');
go
INSERT ...

create table time_testing ( ti TIME );
INSERT INTO time_testing VALUES('');
go
INSERT ...

** The insertion subsequently affects the existing FORMAT date function tests with various arguments for tables date_testing, time_testing.

select * from date_testing;
go
~~START~~
date
1900-01-01
...

select FORMAT(d, 'd','en-us') from date_testing;
GO
~~START~~
nvarchar
1/1/1900
...

• Other date functions

select CONVERT(varchar(30), CAST('' AS date), 102);
go -- 1900.01.01
select TRY_CONVERT(varchar(30), CAST('' AS date), 102);
go -- 1900.01.01
select datepart(day, cast('' as date));
go -- 1
select datediff(year, CAST('1900-01-01'AS date), CAST(''AS date));
go -- 0
select DAY(CAST('' AS date));
go -- 1
select YEAR(CAST('' AS date));
go -- 1900

• Additional cast to other date types

select CAST(CAST('' AS date) AS datetime)
go -- datetime 1900-01-01 00:00:00.0
select CAST(CAST('' AS time) AS datetime)
go -- datetime 1900-01-01 00:00:00.0
select CAST(CAST('' AS date) AS datetime2);
go -- datetime2 1900-01-01 00:00:00.0000000
select CAST(CAST('' AS time) AS datetime2);
go -- datetime2 1900-01-01 00:00:00.0000000
select CAST(CAST('' AS time) AS smalldatetime);
go -- smalldatetime 1900-01-01 00:00:00.0
select CAST(CAST('' AS date) AS smalldatetime);
go -- smalldatetime 1900-01-01 00:00:00.0
select CAST(CAST('' AS date) AS datetimeoffset);
go -- datetimeoffset 1900-01-01 00:00:00.0000000 +00:00
select CAST(CAST('' AS time) AS datetimeoffset);
go -- datetimeoffset 1900-01-01 00:00:00.0000000 +00:00

• Boundary conditions -

• Arbitrary inputs -

• Negative test cases -

• Minor version upgrade tests -

• Major version upgrade tests -

• Performance tests -

• Tooling impact -

• Client tests -

Check List

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is under the terms of the Apache 2.0 and PostgreSQL licenses, and grant any person obtaining a copy of the contribution permission to relicense all or a portion of my contribution to the PostgreSQL License solely to contribute all or a portion of my contribution to the PostgreSQL open source project.

For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[coveralls]

Pull Request Test Coverage Report for Build 15496457607

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 75.456%

---

Files with Coverage Reduction	New Missed Lines	%
contrib/babelfishpg_tds/src/backend/tds/tdscomm.c	2	76.03%

Totals
Change from base Build 15464616681:	0.002%
Covered Lines:	48783
Relevant Lines:	64651

---

💛 - Coveralls

[RIC06X]

LGTM

[Anikait143]

Please add following Test Cases:

1. Tests with empty strings consisting of whitespapces/tabs/new lines.
2. Declare/Select statements
3. Insertion into table with date/time column
4. Casts from string datatypes (empty string) to date/time.
5. Test with Views