Support for weak binding views to allow dropping of underlying objects

[R4hul04]

Description

Currently, Babelfish only supports strong binding for views, which prevents dropping or altering referenced objects when views depend on them. This behavior differs from SQL Server, which by default allows dropping underlying tables or views unless WITH SCHEMABINDING is explicitly specified.
With this change, Babelfish now supports configurable view binding modes:

1. Strong binding (default): Prevents dropping referenced objects if views depend on them
2. Weak binding: Allows dropping of referenced objects

This feature aligns Babelfish more closely with SQL Server's behavior, providing greater flexibility
Key aspects include:

• A new GUC parameter babelfishpg_tsql.weak_view_binding to control the default binding behavior (default is false)
• Support for explicit WITH SCHEMABINDING to create strongly bound views regardless of the GUC setting
• Ability to create weakly bound views by default when the GUC is enabled
• Proper handling of ALTER VIEW operations in both binding modes

In SQL Server, views are weakly bound by default, allowing underlying objects to be dropped or altered. With our implementation, users can now choose between SQL Server's default behavior (weak binding) or the previously enforced behavior (strong binding).

Important Limitation :

This implementation currently only addresses DROP operations on tables, views, functions, procedures as well as ALTER operations on views when these objects are bound by dependent views. ALTER TABLE/ ALTER FUNCTION operations (such as dropping columns or changing data types) are still restricted when dependent views exist, regardless of binding mode. This differs from SQL Server's behavior, where weak binding also allows ALTER operations on referenced objects.
When the same underlying object is recreated, its broken child view will get repaired only if it follows postgresql restrictions for CREATE OR REPLACE VIEW. [The new query must generate the same columns that were generated by the existing view query (that is, the same column names in the same order and with the same data types), but it may add additional columns to the end of the list]
https://www.postgresql.org/docs/current/sql-createview.html#:~:text=The%20new%20query,be%20completely%20different.

Issues Resolved

BABEL-1660

Signed-off-by: Rahul Parande rparande@amazon.com

Test Scenarios Covered

• Use case based -

CREATE TABLE view_test.base_table1 ( id INT, name VARCHAR(50) );
GO

SELECT set_config('babelfishpg_tsql.weak_view_binding', 'true', false)
GO

set_config                                                                                                                                                                                                                                                      
------------
on

CREATE VIEW view_test.weak_view as select * from view_test.base_table1;
GO

DROP TABLE view_test.base_table1
GO

SELECT * FROM view_test.weak_view
GO
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
relation "view_test.base_table1" does not exist

CREATE TABLE view_test.base_table1 ( id INT, name VARCHAR(50), address VARCHAR(50));
GO

SELECT * FROM view_test.weak_view
GO
id         name                                              
------ -------

SELECT * FROM view_test.weak_view
GO
id         name       address                                       
----- --------- -----------

CREATE TABLE view_test.base_table2 ( id INT, name VARCHAR(50));
GO

CREATE FUNCTION view_test.sample_function() RETURNS TABLE AS RETURN ( SELECT id, name FROM view_test.base_table2 );
GO

SELECT set_config('babelfishpg_tsql.weak_view_binding', 'true', false)
GO

CREATE VIEW view_test.weak_view_function AS SELECT * FROM view_test.sample_function();
GO

DROP FUNCTION view_test.sample_function();
GO

SELECT * FROM view_test.weak_view_function;
GO
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
function view_test.sample_function() does not exist

-- Recreate the function 
CREATE FUNCTION view_test.sample_function() RETURNS TABLE AS RETURN ( SELECT id, name FROM view_test.base_table2 );
GO

SELECT * FROM view_test.weak_view_function;
GO
id        name 
----- --------

• Boundary conditions -

-- Recreate the function which selects lesser columns that previous definition
CREATE FUNCTION view_test.sample_function() RETURNS TABLE AS RETURN ( SELECT id FROM view_test.base_table2 );
GO

SELECT * FROM view_test.weak_view_function;
GO
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
cannot drop columns from view

CREATE TABLE t1 ( id INT IDENTITY(1,1) PRIMARY KEY, name TEXT NOT NULL );
GO

CREATE FUNCTION fnc_dependancy_check (@param1 NVARCHAR(100), @param2 NVARCHAR(100), @param3 NVARCHAR(100)) RETURNS NVARCHAR(300) AS BEGIN RETURN @param1 + ' - ' + @param2 + ' - ' + @param3; END;
GO

CREATE VIEW v1 AS SELECT id, fnc_dependancy_check(name, 'ex1', 'ex2') AS example FROM t1;
GO

DROP FUNCTION fnc_dependancy_check;
GO

-- Recreate the function with different input argument or different return parameter

CREATE FUNCTION fnc_dependancy_check (@param1 NVARCHAR(100), @param2 NVARCHAR(100), @param3 NVARCHAR(100)) RETURNS INT AS BEGIN RETURN @param1 + ' - ' + @param2 + ' - ' + @param3; END;

SELECT * FROM v1;
GO
Msg 33557097, Level 16, State 1, Server BABELFISH, Line 1
cannot change data type of view column "example" from nvarchar to integer

• 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 16226896383

Details

• 359 of 388 (92.53%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 76.022%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
contrib/babelfishpg_tsql/src/catalog.c	22	28	78.57%
contrib/babelfishpg_tsql/src/hooks.c	301	324	92.9%

Totals
Change from base Build 16219927312:	0.09%
Covered Lines:	49907
Relevant Lines:	65648

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💛 - Coveralls

[tanscorpio7]

Who sets the flag for alter view case ?