Restore compatibility with SQLServer 2008 R2 in migrations

[zeripath]

This fixes two problems with MSSQL:

• ALTER TABLE DROP ... IF EXISTS ... is only supported in SQL Server >16.

The IF EXISTS here is a belt-and-braces and does not need to be present. Therefore
can be dropped. Also stop attempting to drop the indexes as constraints as they're indexes!

• System tables like: sys.indexes should be lowercase not uppercase because of collation issues.

Fix #16625
Fix #13615
Fix #16483

Signed-off-by: Andrew Thornton art27@cantab.net

[lafriks]

This seems to break migrations

[silverwind]

We need to figure out some way of restricting our SQL syntax against the minimum version of SQL Server we will support.

Should probably add that minimum version on CI and then run all migrations/tests against it, that should lead to CI failures in case of incompatible syntax. 2012 is the oldest version supported by MS, but I think only 2017 and above are available for Linux so we might need to set minimum version to 2017 to be able to test it.

[zeripath]

yup it does because it seems that we will need to check if the thing is a constraint or an index.

Damn.

[codecov-commenter]

Codecov Report

Merging #16627 (a0a5cd5) into main (59e6db0) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main   #16627   +/-   ##
=======================================
  Coverage   45.39%   45.40%           
=======================================
  Files         756      756           
  Lines       85279    85279           
=======================================
+ Hits        38713    38717    +4     
+ Misses      40306    40303    -3     
+ Partials     6260     6259    -1     

Impacted Files	Coverage Δ
services/pull/temp_repo.go	30.76% <0.00%> (-3.85%)	⬇️
services/pull/check.go	25.51% <0.00%> (-2.76%)	⬇️
modules/process/manager.go	72.83% <0.00%> (-2.47%)	⬇️
services/pull/patch.go	54.23% <0.00%> (-1.70%)	⬇️
modules/queue/unique_queue_disk_channel.go	47.26% <0.00%> (-1.37%)	⬇️
models/repo_list.go	76.86% <0.00%> (-0.79%)	⬇️
services/pull/pull.go	41.73% <0.00%> (-0.41%)	⬇️
routers/api/v1/repo/pull.go	29.98% <0.00%> (+0.51%)	⬆️
routers/web/repo/view.go	41.52% <0.00%> (+0.57%)	⬆️
modules/queue/workerpool.go	56.87% <0.00%> (+1.90%)	⬆️
... and 4 more

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[zeripath]

Ah that seems to be now working

[lunny]

You can check if the index is exist at first.

[zeripath]

Line 854 only selects the indexes that exist. The IF EXIST is belt and braces and unnecessary. The DROP CONSTRAINT code was only there because of an earlier problem - solved by lines 843-853.