Dialect specific handling of case sensitivity

[machow]

Currently, to workaround tsql issues...

1. AST representations are converted to lowercase
2. Column names are converted to lowercase

In postgres, these are not issues because unquoted column names should be made lowercase in the AST (as the official parser does). This also means that column names tend to be lowercase, too. Using casing is possible, though, so we don't want to convert everything to lowercase for postgres.

[filipsch]

As a sidenote (without completely understanding the entire context and history), I noticed that AS and as for aliasing are treated differently in postgresql, while they shouldn't.

[machow]

I'm not sure I understand, but in case it helps, it looks like table aliases aren't converted to an alias node (but are Unshaped). In this case the "AS" keyword is stored as written, which might be causing the casing issues?

[filipsch]

@machow, yup, that must be it. Thanks for the pointer.