Support empty string handling for date and time datatypes

[manisha-deshpande]

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:

• Modified date_in() and time_in() functions in PostgreSQL engine to check for empty input string before ParseDateTime() and if in TSQL dialect, prepare date and time default values adjusting their time struct and converting to respective return type Datums (by calling date2j and tm2time respectively).
  • This approach mirrors the empty string handling logic in the babelfish_common package for datetime, datetime2, datetimeoffset, and smalldatetime datatypes through the use of initializeToDefaultDatetime().
• 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.

Issues Resolved

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

Check List

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