azure-sdk-for-net: [BUG] Blob Storage Query Acceleration SQL API Hard Limit on 49 Explicit Columns

Describe the bug

Using the .NET API to run Query Acceleration there appears to be a hard limit on the explicit selection of 49 columns or less. This is (as far as I can tell) not documented anywhere.

For us, we could have >= 50 columns and would like to select a subset. It doesn’t appear to be related to the query length as using the _1, _2, etc syntax results in the same problem.

Oddly the API works when using the * syntax, with the resulting workaround being that we need to return all the columns. This seems overly limited and I am curious as to if there is some underlying reason behind this?

The query and error is as follows, returned from .NET API, but clearly an error from the underlying Web API.

Expected behavior

Underlying Web API would be changed to allow explicit selection of > 49 columns. If this is impossible, this hard limit should be documented at the Query Acceleration SQL language reference.

Actual behavior (include Exception or Stack Trace)

This query is successful. SELECT _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38, _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49 FROM BlobStorage LIMIT 10

This query is not successful SELECT _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _30, _31, _32, _33, _34, _35, _36, _37, _38, _39, _40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _50 FROM BlobStorage LIMIT 10

Following status is reported from .NET API for the second query:

Exception: Azure.RequestFailedException: Service request failed.
Status: 400 (Syntax error!)
ErrorCode: ErrorProcessingQueryExpression

Headers:
x-ms-error-code: ErrorProcessingQueryExpression
x-ms-request-id: aa82517b-301e-008f-18b0-46dea1000000
x-ms-version: 2020-04-08
x-ms-client-request-id: e496a041-8045-4093-a2bf-e129e1e9e3e2
Content-Length: 213
Content-Type: application/xml
Date: Tue, 11 May 2021 22:00:03 GMT
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0

To Reproduce Steps to reproduce the behavior (include a code snippet, screenshot, or any additional information that might help us reproduce the issue)

1. Run the first and second queries above in the .NET API
2. First query will result in success, second in failure

Environment:

• Name and version of the Library package used: Azure.Storage.Blobs 12.8.3
• Hosting platform or OS and .NET runtime version: Windows Server 2016 .NET Framework 4.6.2
• IDE and version : Visual Studio 16.9.4