Set operations: pushdown Take without Offset/OrderBy for SqlServer

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#16,238 3 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp, sql
Domain
database

Research direction

Wait for #16244, then start by reading the provider-specific SelectExpression logic mentioned in the issue. Reproduce a SQL Server set operation using Take without Offset or OrderBy and verify that the generated SQL applies TOP(n) outside a subquery, without changing the SQLite or PostgreSQL behavior.

Written by the indexing model from the issue text.

Description

area-query area-set-operations

Note: this is relevant only after #16244 is done.

Take without Offset+OrderBy is usually translated as TOP(n) for SqlServer, but that isn't possible directly on set operations. We need to push the set operation down into a subquery to apply TOP(n) outside. This depends on provider-specific customization of SelectExpression logic.

On Sqlite and PostgreSQL there's no problem with adding LIMIT 1 directly on the set operation (SELECT 1 AS x UNION SELECT 2 LIMIT 1).

Dominant language
C#
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