anki collection.anki2数据库
flds text not null,
-- the values of the fields in this note. separated by 0x1f (31) character.
-- For example, contains: <question>\x1f<answer>.
sfld integer not null,
-- sort field: used for quick sorting and duplicate check
-- The value of the field having the index 'sortf' as defined by the model
sfld应该是flds的第一个部分(去除了html符号)