mysql的utf8mb4编码的collation应该怎么选择?下面这么多,分别是什么意思? mysql> SHOW COLLATION WHERE Charset = 'utf8mb4'; Collation Charset Id Default Compiled Sortlen Pad_attribute utf8mb4_0900_ai_ci utf8mb4 255 Yes Yes 0 NO PAD utf8mb4_0900_as_ci utf8mb4 305 Yes 0 NO PAD utf8mb4_0900_as_cs ut...