-- | Render an action that must be done on a column.
showAlter :: DBName -> AlterColumn' -> String
showAlter table (oldName, Change (Column n nu t def defConstraintName maxLen _ref)) =
    concat
    [ "ALTER TABLE "
    , escapeDBName table
    , " CHANGE "
    , escapeDBName oldName
    , " "
    , showColumn (Column n nu t def defConstraintName maxLen Nothing)
    ]
showAlter :: DBName -> AlterColumn' -> String
showAlter table (oldName, Change (Column n nu t def defConstraintName maxLen _ref)) =
    concat
    [ "ALTER TABLE "
    , escapeDBName table
    , " CHANGE "
    , escapeDBName oldName
    , " "
    , showColumn (Column n nu t def defConstraintName maxLen Nothing)
    ]
showAlter table (oldName, Change (Column n nu t def defConstraintName maxLen _ref)) =
    concat
    [ "ALTER TABLE "
    , escapeDBName table
    , " CHANGE "
    , escapeDBName oldName
    , " "
    , showColumn (Column n nu t def defConstraintName maxLen Nothing)
    ]