6034 poor index generation on sql server

[tadgh]

• Remove uniqueness constraint
• add migrations
• changelog

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.51%. Comparing base (497b9f2) to head (966acec). Report is 108 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #6035 +/- ## ============================================ + Coverage 83.39% 83.51% +0.11% - Complexity 26927 27324 +397 ============================================ Files 1681 1701 +20 Lines 103965 105762 +1797 Branches 13189 13351 +162 ============================================ + Hits 86702 88326 +1624 - Misses 11613 11729 +116 - Partials 5650 5707 +57 ```

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