babelfish-for-postgresql / babelfish_extensions / 11273659322

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Fixed UDT handling for CASE statement when branch expression is of String Datatype. (#3009)

In CASE expression if we use UDT or sysname in any of the branch, there was no handling to find overall common type
and common typmod for CASE statement. For example, 

create type BABEL_CASE_EXPR_TEST_UDT from NVARCHAR(100);
GO

SELECT 
CASE 2
   WHEN 1 THEN 'abc'
   WHEN 2 THEN CAST('char' AS BABEL_CASE_EXPR_TEST_UDT)
END AS RESULT
GO

output:

Msg 8152, Level 16, State 1, Server BABELFISH, Line 1
value too long for type character varying(3)

Expected output:

nvarchar
char

Changes made to fix the issues - 

We added handling for UDT and sysname for CASE Expression. While finding common type of CASE Expression, we
checked if the following branch is a UDT or not, if yes then find the immediate base_type of UDT and find the TSQL
precedence according to the immediate base_type. If the branch if of type SYSNAME then we directly assign varchar as
datatype for that branch. While finding the common_typmod of CASE Expression, We checked if the branch is a UDT or
not, if yes then find the typmod of the base_type using getBaseTypeAndTypmod().If one of the branch is
of type SYSNAME then set typmod as SYSNAME_TYPMOD (i.e. 128).

Task: BABEL-5103, BABEL-4332
Signed-off-by: yashneet vinayak <yashneet@amazon.com>

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