Fix Mojibake

mojibake.sql

--- the table.the_field contains mojibake
update the_table
  set the_field =
  case
    -- conversion may fail, returning NULL. In this case, retain original data
    when convert(cast(convert(the_field using latin1) as binary) using utf8mb4) is null then the_field
    -- conversion success -> choose the demojibaked data
    else convert(cast(convert(the_field using latin1) as binary) using utf8mb4)
  end