[release/8.x] Produce uncorrelated IN for Contains with nullable item (#32575) #32764
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maumar
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Jan 10, 2024
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Fixes dotnet#32574 (cherry picked from commit 7b712f8)
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Fixes #32574, backports #32575
Description
As a result of the primitive collections changes in 8.0, when Contains is used with a nullable item over a parameterized list, a correlated EXISTS subquery is generated in the SQL. This changes the SQL to contain an uncorrelated IN subquery instead.
Customer impact
The correlated subquery can be the cause of very serious perf regressions; for example, one user reported that a query that previously completed in milliseconds now times out.
How found
Customer reported on 8.
Regression
Yes, considerable perf regression from 7.
Testing
The new SQL is asserted in tests.
Risk
Medium, the change has been quirked.