Shulou(Shulou.com)06/01 Report--

-data type principle try to use integers with small range of values and save storage space: int, bit decimal: decimal represents floating point decimal (5,2) a total of 5 digits, decimal accounts for 2-digit string: varchar (variable length string), char (fixed length string) date time: date, time, datetime enumeration type (enum) attached: string text indicates storage of large text When characters are greater than 4000, it is recommended to use large files such as pictures, audio and video, which are not stored in the database-constraint primary key: primary key physical storage order is not empty: not null unique: unique field does not allow repetition default: default does not fill in the default value, fill in as the quasi-foreign key: foreign key foreign key constraint can ensure the validity of data, but it will reduce the performance of the database when adding, deleting, changing and querying data. Not recommended

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