Add SELECT FOR JSON AUTO support in Babelfish

[Jakeowen1]

Description

This change adds SELECT FOR JSON AUTO support to Babelfish which nests JSON objects based on the structure of the Select statement.

Issues Resolved

BABEL-3668

Test Scenarios Covered

• Use case based -

select U.Id AS "users.userid", O.productId AS "order.productId", O.Id AS "product.oid", P.price AS "product.price" FROM forjson_nesting_vu_t_users U JOIN forjson_nesting_vu_t_orders O ON (U.id = O.userid) JOIN forjson_nesting_vu_t_products P ON (P.id = O.productid) FOR JSON AUTO

[{"users.userid": 1, "o": [{"order.productId": 1, "product.oid": 2, "p": [{"product.price": "20"}, {"product.price": "20"}, {"product.price": "30"}, {"product.price": "30"}]}, {"order.productId": 1, "product.oid": 1, "p": [{"product.price": "20"}, {"product.price": "20"}, {"product.price": "30"}, {"product.price": "30"}]}]}]

• Boundary conditions -

select U.Id AS "users.userid", O.productId AS "order.productId", O.Id AS "product.oid", P.price AS "product.price", S.totalSales AS "totalsales" FROM forjson_nesting_vu_t_users U JOIN forjson_nesting_vu_t_orders O ON (U.id = O.userid) JOIN forjson_nesting_vu_t_products P ON (P.id = O.productid) JOIN forjson_nesting_vu_t_sales S ON (P.price = S.price) FOR JSON AUTO

[{"users.userid": 1, "o": [{"order.productId": 1, "product.oid": 2, "p": [{"product.price": "20", "s": [{"totalsales": 50}, {"totalsales": 50}]}]}, {"order.productId": 1, "product.oid": 1, "p": [{"product.price": "30", "s": [{"totalsales": 100}, {"totalsales": 100}]}]}, {"order.productId": 1, "product.oid": 2, "p": [{"product.price": "30", "s": [{"totalsales": 100}, {"totalsales": 100}]}]}, {"order.productId": 1, "product.oid": 1, "p": [{"product.price": "20", "s": [{"totalsales": 50}, {"totalsales": 50}]}]}]}]

• Arbitrary inputs -

INSERT INTO forjson_nesting_vu_t_sales VALUES (1, NULL, NULL), (2, NULL, NULL);
GO

select U.Id AS "users.userid", O.productId AS "order.productId", O.Id AS "product.oid", P.price AS "product.price", S.totalSales AS "totalsales" FROM forjson_nesting_vu_t_users U JOIN forjson_nesting_vu_t_orders O ON (U.id = O.userid) JOIN forjson_nesting_vu_t_products P ON (P.id = O.productid) JOIN forjson_nesting_vu_t_sales S ON (P.price = S.price) FOR JSON AUTO

[{"users.userid": 1, "o": [{"order.productId": 1, "product.oid": 2, "p": [{"product.price": "20", "s": [{"totalsales": 50}, {"totalsales": 50}]}]}, {"order.productId": 1, "product.oid": 1, "p": [{"product.price": "30", "s": [{"totalsales": 100}, {"totalsales": 100}]}]}, {"order.productId": 1, "product.oid": 2, "p": [{"product.price": "30", "s": [{"totalsales": 100}, {"totalsales": 100}]}]}, {"order.productId": 1, "product.oid": 1, "p": [{"product.price": "20", "s": [{"totalsales": 50}, {"totalsales": 50}]}]}]}]

• Negative test cases -

1> select cast(null as datetime) for JSON AUTO
2> go
json                                                                                                                                                                                                                                                            
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
[{}]                                                                                                                                                                                                                                                            

(1 rows affected)
1> 

• Minor version upgrade tests -
  NA

• Major version upgrade tests -
  Added to upgrade scripts

• Performance tests -
  NA

• Tooling impact -
  NA

• Client tests -
  NA

Check List

• Commits are signed per the DCO using --signoff

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[coveralls]

Pull Request Test Coverage Report for Build 7561344918

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• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 71.821%

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Totals
Change from base Build 7472197412:	0.1%
Covered Lines:	39695
Relevant Lines:	55269

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💛 - Coveralls

[forestkeeper]

Did you mean need to get the first elements of List arg here ?
I think better to write linitial ? or proper function from pg_list.h

[forestkeeper]

Is there any else in here ?

[forestkeeper]

The place to put query tree walker should be after tsql dialect check

[forestkeeper]

In here we should call check_json_auto_walker instead of query_tree_walker to avoid one more stack level.

[forestkeeper]

Please use nodeTag(node) == T_TargetEntry to make the code more readable

[forestkeeper]

What if it's == NULL, in such case we should throw exception ? If so , pls use assert

[forestkeeper]

Otherwise we'll have to write some else clause to cover those

[forestkeeper]

Why we realloc some space in here ?

[Jakeowen1]

We need to allocate space for the new array element being added to jsonbArray

[forestkeeper]

list_nth_cell(aggargs, 1) != NULL

--> should be

list_length(aggargs) > 1 ?

[forestkeeper]

If we're for loop into targetList, why not using foreach( lc , targetlist ) ?

[forestkeeper]

Pls add a

assert(subqRte->rtekind == RTE_RELATION)

in here to make sure we don't miss anything in future

[forestkeeper]

Should add one more test case that inside the trigger like this :

with cte as (
select * from inserted
)
select * from cte as json auto

[forestkeeper]

If we already support for json auto syntax, then we should add this test case into other Mvu schedule files as well.