Fix behavioural differences due to return type and handle constant string literal inputs differently for COALESCE function

[basasairohan]

Description

Behavioural differences mentioned below have been found out better PG Coalesce and T-SQL Coalesce function.

1. Consistency in return datatype i.e., for the same set of input datatypes T-SQL should return consistent return datatype as shown in below example

-- T-SQL
select coalesce(cast(8 as smallint), cast(1 as bit))
go
~~START~~
smallint
8
~~END~~
select coalesce(cast(1 as bit), cast(8 as smallint))
go
~~START~~
smallint
1
~~END~~

-- BBF

select coalesce(cast(8 as smallint), cast(1 as bit))
go
~~START~~
smallint
8
~~END~~
select coalesce(cast(1 as bit), cast(8 as smallint))
go
~~START~~
bit
1
~~END~~

2. When the input is constant string literal i.e., T-SQL should take short circuit evaluation meaning unnecessary arguments should not be evaluated

-- T-SQL
1> SELECT COALESCE(NULL, 1, 2, 'I am a string')
2> go
           
-----------
          1

(1 rows affected)

-- BBF
1> SELECT COALESCE(NULL, 1, 2, 'I am a string')
2> go
Msg 22, Level 16, State 1, Server BABEL, Line 1
invalid input syntax for integer: "I am a string"

This change adds a new function select_common_type_for_coalesce_function to choose the return datatype which will be called from tsql_select_common_type_hook whenever the caller function is T-SQL COALESCE.

Issues Resolved

[BABEL-726]

Engine PR : babelfish-for-postgresql/postgresql_modified_for_babelfish#345

Signed-off-by: Sai Rohan Basa [email protected]

Test Scenarios Covered

• Use case based - babel_726.sql

• Boundary conditions - Yes

• Arbitrary inputs - Yes

• Negative test cases - Yes

• Minor version upgrade tests -

• Major version upgrade tests -

• Performance tests - N/A

• Tooling impact - N/A

• Client tests - N/A

Check List

• Commits are signed per the DCO using --signoff

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[jsudrik]

Cherry pick from the other branch. Approved.