anchor.diff:      -- +.[
               %% '(' -- ws -- +.parenthesized -- ')' -|> id
               %% kw "EXISTS" -- ws -- '(' -- ws -- +.selectStmt -- ')' -|> ExistsExpr
  -            %% +.qualifiedColumnName -|> ColumnNameExpr
               %% +.literal -|> LiteralExpr
               %% +.bindParameter -|> BindParameterExpr
               %% +.cast expr -|> CastExpr
  
positive.code: 
  let private updateStmt =
      let setColumn =
          %% +.nameOrString
          -- ws
          -- '='
          -- ws
  
negative.code: 
  let private asAlias =
      %% (zeroOrOne * kw "AS")
      -? +.name
      -|> id
  
  let private resultColumnCase =
  